Pressed F on a Magnet train ramp (Schedule Skipping) and got this error. It also has completely bricked a multiplayer save and even at an earlier save-state with the mod disabled keeps the desync happening. Server has been played for a week with 0 issues from all mods until I pressed F on the ramp and now it's unplayable. However, creating a brand-new map and save with all mods and Renai enabled yields no errors until another ramp gets interacted with F. Modlist can be linked if mecessary.

The mod Renai Transportation (2.1.0) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event RenaiTransportation::RTInteract (ID 215)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
__RenaiTransportation/script/event/interact.lua:319: in function <RenaiTransportation/script/event/interact.lua:3>

Whops it looks like I forgot to add some checks to the switching code where it will switch the ramp but then also check for other objects after swapping out the original, which is what causes the crash. I'm not sure why it would mess up the save file though, but you can try with the fix on v2.1.1 to see if it helps.

i talked with phantom to get a better understanding of the un recoverable issue. its a Desync issue from the other player when joining. host can load and play other player can play, but they cant play together. which is weird as mods didnt change except for this event.

Whops it looks like I forgot to add some checks to the switching code where it will switch the ramp but then also check for other objects after swapping out the original, which is what causes the crash. I'm not sure why it would mess up the save file though, but you can try with the fix on v2.1.1 to see if it helps.

This fixed the magnet ramp switching mode, BIG FIX! Many thanks! But the entire save is still permanently desync'd and is unplayable in multiplayer. I'm going through all the manual work now to see which mod is actually creating the desync issue, but all I know as of now is the entire save for the last 20 hours of gameplay has been flawless until I ran into that bug the first time.

EDIT: After the first batch of assessing the issues with desync on the server, I have came to the conclusion that the mods causing the desync is kuxynator's Zooming Reinvented Running Mod and/or their required library.

Yeah that's a bizarre one, I have no idea how networking and multiplayer stuff works in mods. Glad to hear the fix works at least 👍