I'm unsure whether this is Stack Combinators (https://mods.factorio.com/mod/stack-combinator) not cleaning up, or if it's not being erased correctly.
Placing a stack combinator in the sandbox and then resetting the sandbox seems to leave behind an entity that causes a crash on load.
The crash comes from the stack combinator mod, but it only happens if you actually reset the sandbox; If you simply remove the combinator without resetting it works just fine.
If this is actually the fault of the other mod I will report it there. Error text:
The mod Stack Combinator (1.2.12) caused a non-recoverable error.
Please report this error to the mod author.
Error while running event stack-combinator::on_tick (ID 0)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
__stack-combinator/scripts/staco/staco.lua:116: in function 'created'
stack-combinator/scripts/runtime.lua:28: in function 'run_combinators'
stack-combinator/scripts/staco/event-setup.lua:64: in function 'handler'
stdlib/stdlib/event/event.lua:342: in function 'pcall'
stdlib/stdlib/event/event.lua:362: in function 'dispatch_event'
stdlib/stdlib/event/event.lua:438: in function <stdlib/stdlib/event/event.lua:396>