Merge all Faces Not Working

Hi, I am trying to merge all coplanar faces in Rhino, but sometimes it works and sometimes it doesn’t, is there a setting that made it unmergeable?

it is on the same surface, under one poly surface solid, but merging all faces didn’t work.

It merged in Rhino 7 but didn’t merge in Rhino 8. Need Help.

Can’t help without the file. Also, why can’t you just recreate this surface?