Jesusemora
Thank you for your reply, I got the issue. The problem was a Spotlight node. The map that works (the second) has multiple omnilights, a little more memory consumed but stable, the one that doesn't work had a spotlight for shadows, just changing the node made all the difference.

The 'map meshes' part, i was wondering if any z-fighting or colliding objects could cause the problem.
The meshes had materials, no shaders that I had pud on as next-pass or whatever.
I am using the OccluderInstance3D node for hiding objects that don't need to be drawn.
1 - i5 8° gen, rx 550, windows
2 - vulkan
3 - 4.3
4 - 30 actually, all 'integer division, rest will be discarded'
5 - Yes using shadows, idk why the spotlight in specific was causing that problem, but it was set for 300m range, while omnilights with the same settings work fine
6 - 600
7 - less than 200 in the scene, logical, meshes and collision shapes
8 - Actually yes, I'll look more into it now that you mention it as not being suitable, I made the map on trenchbroom, imported to edit in blockbench, and into godot. Multimesh setting came as default and posed no problems until now
Again, thank you for your time!