The mod Belt Balancer 2 (2.0.9) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event belt-balancer-2::on_player_mined_entity (ID 68)
belt-balancer-2/objects/part.lua:265: attempt to index local 'belt' (a nil value)
stack traceback:
belt-balancer-2/objects/part.lua:265: in function 'remove'
belt-balancer-2/control.lua:145: in function <belt-balancer-2/control.lua:134>

Happens when trying to move/pickup the belt balancer after it seemingly glitched out, even roboports can't move it.
Am able to add+remove more belt balancers around it except for the bottom side.
Attempting to connect an input on the bottom side causes it to crash. Happened on fulgora.

I have a similar issue.

Error while running event belt-balancer-2::on_player_mined_entity (ID 68)
belt-balancer-2/objects/part.lua:215: attempt to index local 'belt' (a nil value)
stack traceback:
belt-balancer-2/objects/part.lua:215: in function 'remove'
belt-balancer-2/control.lua:145: in function <belt-balancer-2/control.lua:134>

I also have a Splitter leading to it that I cannot remove:

Error while running event belt-balancer-2::on_nth_tick(8)
LuaTransportLine API call when LuaTransportLine was invalid.
stack traceback:
[C]: in function 'len'
__belt-balancer-2/objects/balancer.lua:203: in function 'run'
belt-balancer-2/helper/message-handler.lua:33: in function <belt-balancer-2/helper/message-handler.lua:31>

I had the same problem too, i have make personal fix probably not the most clear code ever but this make job and escape the crash
https://drive.google.com/file/d/10RIeE1AnFmGKMdNMOk4ikbjkm1dBRTRx/view?usp=drive_link

Doesn't seem to solve my problem. But much appreciated.

fix based on crash part.lua:265 and sub fix of same crash

never good report diferent crash in same post