Well not sure what to tell you, but when the game is booted to start, the exe is still there. When trying to join a friends game, it crashes and the exe is gone.

Malwarebytes and already checked that. If it was an antivirus thing then it would have occurred the moment I tried to open the game. But I had been playing for 2 weeks before this started.

So its just like the title claims, when I try to load into a friends world, almost every time recently, the factorio.exe simply goes missing from
C:\Program Files (x86)\Steam\steamapps\common\Factorio\bin\x64

This will also occur when I try to apply/disable mods in single player. My initial thought ...