The mod Belt Balancer (Improved Performance) (3.1.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event belt-balancer-performance::on_nth_tick(8)
invalid key to 'next'
stack traceback:
[C]: in function 'next'
belt-balancer-performance/objects/balancer.lua:214: in function 'run'
belt-balancer-performance/helper/message-handler.lua:33: in function <belt-balancer-performance/helper/message-handler.lua:31>

Just realized it wasnt updated, will report back if that fixes it.

That fixed it, of course.