Known Conflicts - TeamOpenIndustry/ImmersiveRailroading GitHub Wiki
Certain Mods / Configurations are known to cause conflicts
Bungee/Waterfall:
You will need to change a Waterfall config option relating to entity IDs across servers. See https://github.com/cam72cam/ImmersiveRailroading/issues/579 and https://github.com/PaperMC/Waterfall/issues/136 for more details.
ViveCraft
Since ViveCraft messes with the minecraft graphics internals, a lot of the functionality is known to break in unexpected ways.