I think the case is like the following. There exists a splitter adjancent to a balancer (both exits go into a balancer; one directly, one via 1 piece of belt). If I remove FIRST the balancer, and THEN the splitter, the game crashes.

9484.240 Error MainLoop.cpp:1288: Exception at tick 11165937: Мод Belt Balancer (Improved Performance) (3.1.3) вызвал неустранимую ошибку.
Пожалуйста, сообщите об этой ошибке автору мода.

Error while running event belt-balancer-performance::on_nth_tick(4)
LuaTransportLine API call when LuaTransportLine was invalid.
stack traceback:
[C]: in function 'len'
__belt-balancer-performance/objects/balancer.lua:198: in function 'run'
belt-balancer-performance/helper/message-handler.lua:33: in function <belt-balancer-performance/helper/message-handler.lua:31>

https://github.com/archiecarrot123/belt-balancer/pull/1 fixed