For some reason, I'm not abel to place traintracks in the sub area only modded ones.
Also, When I want do ride down, I get this error:
The mod Subsurface - build beneath your base! (1.1.6) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Subsurface::on_tick (ID 0)
LuaEntity belongs to surface nauvis (index 1) but a LuaEntity belonging to surface nauvis_subsurface_1 (index 3) was expected.
stack traceback:
[C]: in function 'newindex'
__Subsurface/scripts/trains.lua:121: in function 'handle_subways'
Subsurface/control.lua:339: in function <Subsurface/control.lua:326>

Let me know if you need a save file or not (or any other stuff)

Yes please send me a save file with only my mod and other mods causing the error

Here is the file.
https://drive.google.com/file/d/1Vemb1NY3kWd4JKKh-CDslaXbiPgFZQbN/view?usp=sharing
However, I'm also unable to place Train Tracks. Only moded ones.
https://imgur.com/a/nAnpf4j
My Mods, which affect the Rails and Signals:
Base Mod > Minimal Electric Rails > Space Age > Muluna, Moon of Nauvis > Schall Overseas Railway > Janus > Subserface > Maraxsis
Can one of them be the culprit, that I can't place it underground?

One more issue:
When I want to get a BP-Book, I get this error:
The mod Subsurface - build beneath your base! (1.1.6) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Subsurface::on_player_cursor_stack_changed (ID 36)
Subsurface/scripts/elevators.lua:121: attempt to index local 'blueprint' (a nil value)
stack traceback:
Subsurface/scripts/elevators.lua:121: in function 'elevator_on_cursor_stack_changed'
Subsurface/control.lua:576: in function <Subsurface/control.lua:575>

About the rail placement, this is caused by another mod.
About the blueprint issue, I can't reproduce.

Rail, okay
BP, just did. Interestingly, I had a BPB, where I did not have a selected BP in it. Copy into the inventory and then choose one. That fixed the issue. Interestingly, only this BPB was the issue. All others were fine.

The train thing will be fixed in the next release