Have been playing FTB Revelations 3.2.1, which includes IE 0.12-91 in it on a multiplayer server -- Have had several players reach a few different area's in the map where we crash to desktop from Ticking Block Entity's, ArrayIndexOutOfBoundsException: 0 pointed at the Diesel Generator

I gathered a few couple crash reports myself - only workaround we can find right now is to get moved somewhere else while offline and then never go back to the locations. The crash reports I have are from the same location on the map, but there are other locations as well with the same crash dumps.

Crash dump 1 (first loading the area): https://pastebin.com/raw/Wp4QUADz
Crash dump 2 (trying to log back in a second time after the first crash without changing player location): https://pastebin.com/raw/yPUsGPG2

I went ahead and created a single player world (brand new world) in the same modpack (so same mods as the crash dump lists), crafting it in the world did not have the same issue.

snippet -
`Description: Ticking block entity

java.lang.ArrayIndexOutOfBoundsException: 0
at blusunrize.immersiveengineering.common.blocks.TileEntityMultiblockPart.isDummy(TileEntityMultiblockPart.java:284)
at blusunrize.immersiveengineering.common.blocks.metal.TileEntityDieselGenerator.func_73660_a(TileEntityDieselGenerator.java:83)
at net.minecraft.world.World.func_72939_s(World.java:1838)
at net.minecraft.client.Minecraft.func_71407_l(Minecraft.java:1847)
at net.minecraft.client.Minecraft.func_71411_J(Minecraft.java:1098)
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:398)
at net.minecraft.client.main.Main.main(SourceFile:123)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
`

Let me know if there's more info I can provide, I tried to capture everything I could

Sounds like there's bad tile entity data for that block or something, perhaps. Below the trace you've posted it prints the block position (3174 60 3451) you could try /setblocking it to air or the like. Potentially use /fill to only replace the multiblock blocks to prevent destroying others.

I'll have to harass the staff team to try to do that, that would be a potential workaround since they shouldn't have any issue with that...

any updates?

The update is: We don't support 1.12 anymore.