This is my modpack and crashing process:
https://imgur.com/a/odEExda

The mod Factory Efficiency Tracker (0.1.1) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event factory-efficiency-tracker::on_tick (ID 0)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
__factory-efficiency-tracker/scripts/stats.lua:56: in function 'update_stats'
factory-efficiency-tracker/scripts/stats.lua:106: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>

Sweet. Can you send me a savefile to sync all the mods?

Hi,

I was having the same issue but fixed it temporarily by inserting a check at line 58 in stats.lua:

if not (entity and entity.valid) then return end -- FIXME: temporary fix due to invalid entities getting into global.schedule

Not sure why invalid entities are present at that point in the code, but I did make a couple map changes with the map editor, which could be why in my case.