I guess it's about the "Safety; Increase wall resistance to spitters" setting.
However, I don't get this error either in pure "Rampant Fixed" or in combinations with popular mods like K2.
You may have added mods that add walls that are very different from the standard ones (for example, laser fences).
I would like to get a save, so as not to guess with which mod the incompatibility happened.
Until the incompatibility is resolved, I recommend removing the check mark in the setting "Safety; Increase wall resistance to spitters".
If I remember correctly, when a loading error occurs, the option "reset settings to default" appears. You can use it.