New GZDoom breaks my level. :(

I'm confused.  A level that tests perfectly well in 3.72 is messed up in the latest build.  I copied it to the new folder twice to make sure something didn't get broken in the copying process.  Floor heights seem to be moved around and a 3D floor that was used to make a bridge now appears in other sectors as well.  Why does this happen?  What has been done to 4.1.2 to break 3D floors?

Hard to tell without being able to look at the map.

It's the third level of this set: https://www.moddb.com/mods/rabids-levels-v03/downloads/e1m1-3b

Take a look at this recent thread. It discusses your problem and the problem has apparently been resolved. 

I hope that it works for you too

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The problems with your map are:

1. Invalid data encountered for texture E1M1-3B.pk3:textures/blood1

etc.

2. Script warning, "E1M1-3B.pk3:decorate" line 30:
Unknown class name 'LightShaft2bRIGHTER' of type 'Actor'

etc.

3. Script error, "E1M1-3B.pk3:voxeldef"line 1:
Voxel "ammoa" not found.

etc.

4. referencing these 3 linedefs to every sector with tag 0

and maybe the overuse of shaders, but that is a matter of personal preference.

Thanks.  I'm not sweating problems that GZDoom cries about before it loads that don't have a practical impact after (though I am working on fixing them anyway).  Curious about opinions on the levels themselves, but really just looking for a solution to that crazy floor.  I'll fix it now that I know what's wrong.  As for the rest, all I can say is that these levels have some evolution ahead of them for sure.  Not less shaders, because a large part of the theme is lighting everything 100% dynamically, which I'm sure is not to everyone's taste.