I can't answer much, but everytime I had unknown graphical glitches in my maps, slime trails, wonky collision etc(one time I reached a line limit or something and every new sector I made after that point had no collision, or it looked like you would get sucked into it when close) I switched to,
ZDBSP Compressed nodes (udmf) (large maps)
Emphasis on large maps cuz they get real wonky if you don't have the right node builder.