Why surface is deviding into triangles?Please help😭

I was working on this model for 2 weeks there was no any problem, today I was simply trying to create a wall and create a window in the wall, so I’ve created a surface and trying to cut off the window in the surface it doesn’t work, just line not intersecting with surface, after I decided to divide surface into small section and suddenly its ripped into small triangles. I’ve tried to recreate the whole new surface but still same problem :sleepy:

Upload the .skp file so we can see what you’ve got. It looks like you’ve cot some edges slightly out of plane.