The problem you are having is pretty different, I'd like to help you solve it I can, but need information since "R_Renderview: NULL worldmodel" -- should be almost impossible as error with a valid map.

1) Are you playing regular Quake or a Mission Pack or something else or a specific map?
1b) If not regular, what are typing in to play it?

2) Are you using replacement content?
2a) Are you using .lit and .vis from the download?

(NightFright supplied that I haven't personally tested it, but he's very thorough but if put in the wrong folder could cause problems.)

3) You are on Windows using the current version at quakeone.com/markv?

4) Could you post your config.cfg, autoexec.cfg and qconsole.log (when it crashes)? 

To make sure everything is in order I made a new directory, only id1 folder with pak0.pak and pak1.pak and the mark v files (also downloaded again). I started the game on normal, entered the portal and saved at the slipgate complex. If I start mark v and attempt to load the game from the menu I get the crash.

1)Just pak.0.pak and pak1.pak from the gog installation, no mods installed no changes in config, no autoexec.

2)none

3)win10 home 64bit, yes newest version, both opengl and software crash.

4)config.cfg (default, made no changes for the purpose of this test)
// Mark V
unbindall
bind "TAB" "+showscores"
bind "ENTER" "+jump"
bind "ESCAPE" "togglemenu"
bind "SPACE" "+jump"
bind "+" "sizeup"
bind "," "+klook"
bind "-" "sizedown"
bind "." "+mlook"
bind "0" "impulse 0"
bind "1" "impulse 1"
bind "2" "impulse 2"
bind "3" "impulse 3"
bind "4" "impulse 4"
bind "5" "impulse 5"
bind "6" "impulse 6"
bind "7" "impulse 7"
bind "8" "impulse 8"
bind "=" "sizeup"
bind "[" "impulse 10"
bind "]" "impulse 12"
bind "`" "toggleconsole"
bind "a" "+moveleft"
bind "d" "+moveright"
bind "e" "+movedown"
bind "q" "+moveup"
bind "s" "+back"
bind "t" "messagemode"
bind "w" "+forward"
bind "~" "toggleconsole"
bind "CTRL" "+attack"
bind "ALT" "+strafe"
bind "SHIFT" "+speed"
bind "PAUSE" "pause"
bind "LEFTARROW" "+left"
bind "RIGHTARROW" "+right"
bind "UPARROW" "+forward"
bind "DOWNARROW" "+back"
bind "PGUP" "+lookup"
bind "PGDN" "+lookdown"
bind "END" "centerview"
bind "F1" "help"
bind "F2" "menu_save"
bind "F3" "menu_load"
bind "F4" "menu_options"
bind "F5" "menu_multiplayer"
bind "F6" "echo Quicksaving...; wait; save quick"
bind "F9" "echo Quickloading...; wait; load quick"
bind "F10" "quit"
bind "F12" "screenshot"
bind "MOUSE1" "+attack"
bind "MOUSE2" "+forward"
bind "MOUSE3" "+zoom_key"
bind "MWHEELUP" "impulse 10"
bind "MWHEELDOWN" "impulse 12"
_cl_color "0"
_cl_name "player"
_cl_sky ""
_hd_folder "hd"
_snd_mixahead "0.1"
bgmvolume "1"
capturevideo_codec "auto"
capturevideo_console "1"
capturevideo_fps "30.0"
capturevideo_hack "0"
capturevideo_mp3 "0"
capturevideo_mp3_kbps "128"
cfg_unbindall "1"
cl_anglespeedkey "1.5"
cl_autodemo "0"
cl_backspeed "400"
cl_bob "0.02"
cl_bobcycle "0.6"
cl_bobside "0.02"
cl_bobsidecycle "0.9"
cl_bobsideup "0.5"
cl_bobup "0.5"
cl_forwardspeed "400"
cl_maxpitch "90"
cl_minpitch "-90"
cl_movespeedkey "2.0"
cl_pitchspeed "150"
cl_rollangle "2.0"
cl_sidebobbing "0"
cl_sidespeed "350"
cl_upspeed "200"
cl_yawspeed "140"
contrast "1"
crosshair "0"
cutscene "1"
external_music "1"
fov "90"
gamma "1.0"
gl_polyblend "1"
host_maxfps "72"
host_sleep "0"
host_startdemos "1"
in_freelook "1"
in_keymap "1"
in_system_enhanced_keys "1"
lookspring "0"
m_filter "0"
m_forward "1"
m_pitch "0.022"
m_side "0.8"
m_yaw "0.022"
nomouse "0"
pq_bindprotect "0"
pq_download_http_locs "1"
r_clearcolor "2"
r_lavaalpha "1"
r_mirroralpha "0.2"
r_slimealpha "0.7"
r_stains "1"
r_viewmodel_fov "90"
r_viewmodel_offset "0"
r_viewmodel_quake "0"
r_viewmodel_ring "0"
r_viewmodel_size "0"
r_wateralpha "0.5"
r_waterripple "0"
r_waterwarp "1"
saved1 "0"
saved2 "0"
saved3 "0"
saved4 "0"
savedgamecfg "0"
scr_clock "-1"
scr_conspeed "300"
scr_originalquake2d "0"
scr_sbaralpha "1"
scr_sbarcentered "1"
scr_scaleauto "1"
scr_showfps "0"
sensitivity "3"
sndspeed "11025"
sv_aim "0.93"
sv_altnoclip "1"
sw_sky_load_skyboxes "1"
v_gunkick "1"
v_kickpitch "0.6"
v_kickroll "0.6"
v_kicktime "0.5"
v_polyblend_lite "0"
v_smoothstairs "1"
vid_fullscreen "0"
vid_height "480"
vid_refreshrate "60"
vid_sound_thread "1"
vid_stretch "1"
vid_vsync "0"
vid_width "640"
viewsize "100"
volume "0.7"

no autoexec file

qconsole.log

Command line: [ ]
Log file: D:\test/id1/qconsole.log
Sat Nov 19 23:32:18 2016
WinQuake Mark V Windows (Build: 900)
Exe: mark_v_winquake.exe (1064 kb)
Exe: 14:43:15 Nov 18 2016
Caches: C:/Users/myname/AppData/Roaming/Mark V/caches
UDP4 Initialized: INADDR_ANY, 192.168.0.12
IPv6 Initialized: [fe80:0:0:0:9d90:b865:2c23:5f89%5]
Exe: 14:43:00 Nov 18 2016
256.0 megabyte heap
joystick not found -- no valid joysticks (a5)
Input initialized
Avi capturing module initialized
ACM module initialized

Sound Initialization
Set primary sound buffer format: yes
Using secondary sound buffer
2 channel(s)
16 bits/sample
11025 bytes/sec
DirectSound initialized
Audio: 16 bit, stereo, 11025 Hz
Sound sampling rate: 11025
CDAudio_Init: No CD in player.
CD Audio Initialized

========= Quake Initialized =========

execing quake.rc
execing default.cfg
execing config.cfg
couldn't exec autoexec.cfg
3 demo(s) in loop
Playing demo from demo1.dem.



the Necropolis
Using protocol 15
You got the shells
You got the Grenade Launcher
Loading game from D:\test/id1/s0.sav... 

Can you upload this save game file and both of your pak files?

This is very weird and I'd like to examine this. 

I just checked it with rogue/pak0.pak, same deal, if I save in the expansion next time I enter the game when I try to load I get the error.

Same exact files work fine with 20160915 version of mark v (checked again now just to be sure, fresh folder etc).

If you wish I can upload the files but I think this proves they're not the issue here. 

I need the files uploaded if I am to have any chance of examining your problem and solving it.

Keep in mind several people have used both the Open GL and WinQuake versions. 

https://ufile.io/47125 

Going to take a look at this.

Cross your fingers and hope I can experience this problem. I have my fingers crossed.

/Otherwise, I can't think of any way I can help :( 

I'm getting the same kind of crash. It seems that the demo playback is causing it. Starting a singleplayer game or simply not running anything makes the savegame work. 

With your pak files and your save game I can reproduce your problem.

It appears to be your pak files, somehow. Your pak0.pak in particular is not the same size. Your pak1.pak appears to be the same as mine.

Your save game does not cause me problems with my pak files.

I'll have to come up with a plan to figure out what is different and why it is happening.

/It's getting late and I'll probably do that tomorrow. But looks good that I'll be able to solve your problem. 

Pretty awesome I can reproduce problem and if you are getting it too, that helps.

I'm not getting problem with my own pak files.

And he says slightly older Mark V didn't have issue.

So I'll see what solves this little mystery and what is going on. 

/But it's late. Tomorrow sometime is most likely time. 

Pak sizes in my installation:

pak0 18312419
pak1 34362368

They're different on my CD:

pak0 18689235
pak1 34257856

I checked and, as expected, the difference is applying the vis patch. Regardless, the paks copied from the CD didn't fix the crashing for me (which is present in mods like Malice as well). 

There's currently a hard limit on the number of polygons a model can have at 2048, and unfortunately that means some model packs don't really work now. I don't see why that's in there, perhaps that cap can be removed? 

I've thought about the model limits. Quakespasm Spiked, for instance, loosens those up, and Enhanced GLQuake and I believe JoeQuake had higher limits.

In trying to get to the engine out beta stage to release Quake stage, I decided to skip thinking about that in the current release.

FitzQuake 0.85 has compatibility warnings (*), and I'd want to make sure a compatibility warning printed and also make sure no consequences in the software render (WinQuake) version of Mark V.

Short version: Something I care about but decided to not address before doing the release.

Is it an issue? It sure is. I know of replacement models that won't work.

--
(*) which new Mark V mirrored the Quakespasm approach to only print those if developer is set to 2 or higher 

I'll address this in some form in the next 24 hours. 

According to Enhanced GLQuake/Enhanced WinQuake by Ben Jardrup ...

He raised the vertex limit to 3984 with the comment 3985 or higher seems to crash assembler (?) ... (means WinQuake's assembly language code).

So looks like I'm going to use 3984 as the new vertex limit which is about double current limits.

He raised the triangle limit to from 2048 to 4096. So I'll increase to that limit.

So both of those limits will about double, and it will be compatible with both the Open GL version and the WinQuake version.

(Ben Jardrup wrote one of the most backwards compatability-minded and thoughtful engines ever. Widely used until FitzQuake 0.85 came out with a similar limit raising capabilities). 

New version update, details in the new thread

http://celephais.net/board/view_thread.php?id=61375

This thread should really be closed and I'm going to post in General Abuse ask if a moderator could do that.

/Crazy to have 2 threads open.