I am not sure what causes it,:

"Mod Factorissimo 2 - notnotmelon fork (1.1.4) orsakade ett oreparerbart fel.
Vänligen rapportera detta fel till mod-författaren.

Error while running event factorissimo-2-notnotmelon::on_nth_tick(30)
invalid key to 'next'
stack traceback:
[C]: in function 'for iterator'
factorissimo-2-notnotmelon/script/travel.lua:88: in function <factorissimo-2-notnotmelon/script/travel.lua:87> "

I have tested some things and the crashes seem to happen when I have an companion drone with me in my base. I can run around without one without anything happening but as soon as I assemble a companion drone and start running in the base the crash happens.

Can verify - running factorissimo 2 and companion drones crashes sometimes when entering / exiting factorioes or when a companion drone collides with / flies over a factory. If not crashing it can also destroy drones doing these same actions.
Reverting back to 1.0.13 fixes the issue.

Companion Drone is a spider-vehicle so probably related to spidertron changes in 1.1.3

Can confirm that the error occurred when spidertron was leaving factory building.
Mod Version 1.1.4

Fixed for the next release. Thanks for the reports

Fixed. Spidertron could exit the building without crashing.

I also dont have a problem with the companion drones anymore so my issue were fixed.