Oooh...

In a vehicle crossing other tiles I get no damage but after stopping I get damaged and the same thing happens after exiting the vehicle as if mod behavior has changed.

Train on fire

You should take some damage while on non-manmade tiles and when you stop moving the floor will light on fire, doing more damage (this is the same while in a vehicle except you will take less damage since the vehicle provides some cover). Maybe you have power armor on which is absorbing the damage?

I constantly got damaged before on non-man made tiles if I don't interact with vehicles.

I checked again with the same parameters and the result is another.

No matter where I am on non-man made tiles if I stopped, I will get damaged.

╮('～';)╭ maybe often taking damage is more about lava?

For example, checking every ~300 ticks with a 600 tick lava buff applied