142307.919 Error MainLoop.cpp:1284: Exception at tick 74184380: The mod Belt Balancer (Improved Performance) (3.1.3) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event belt-balancer-performance::on_player_mined_entity (ID 67)
belt-balancer-performance/objects/part.lua:253: attempt to index local 'belt' (a nil value)
stack traceback:
belt-balancer-performance/objects/part.lua:253: in function 'remove'
belt-balancer-performance/control.lua:165: in function <belt-balancer-performance/control.lua:154>
142307.919 Error ServerMultiplayerManager.cpp:92: MultiplayerManager failed: "The mod Belt Balancer (Improved Performance) (3.1.3) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event belt-balancer-performance::on_player_mined_entity (ID 67)
belt-balancer-performance/objects/part.lua:253: attempt to index local 'belt' (a nil value)
stack traceback:
belt-balancer-performance/objects/part.lua:253: in function 'remove'
belt-balancer-performance/control.lua:165: in function <belt-balancer-performance/control.lua:154>"
142307.920 Info ServerMultiplayerManager.cpp:797: updateTick(74184380) changing state from(InGame) to(Failed)
142307.926 Quitting: multiplayer error.

It would appear that you have removed a balancer part with an invalid output belt. Some more context would be helpful, for example if you had placed a belt weirdly or rotated a belt in-place (with r key).

Sorry for the late reply.

I don't think I can reproduce this situation again. Since then, there have been no such problems.