Is this the seam you mean?
https://imgur.com/a/IrMnN
Are the faces that meet in the rectangle I drew phong shaded? Are they on the same plane?
I guess it's the sample-point-positioning code not working properly. Is the map sealed? Sealing it may help if it's not.
Aside from that all I can suggest is tweak the geometry. Unfortunately there's no easy fix on the tools side and any time I adjust this code it tends to break some maps and make others better.
In general it looks like 0.15.9 was the sweet spot. I would revert to that but it can't handle faces that are partially covered, e.g. func_detail_wall.