Placing a belt as output, inside a tier 1 building

The mod Factorissimo 2 - notnotmelon fork (1.2.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event factorissimo-2-notnotmelon::on_built_entity (ID 6)
factorissimo-2-notnotmelon/script/connections/belt.lua:69: attempt to index local 'outside_link' (a nil value)
stack traceback:
factorissimo-2-notnotmelon/script/connections/belt.lua:69: in function '?'
...ssimo-2-notnotmelon__/script/connections/connections.lua:133: in function 'init_connection'
...ssimo-2-notnotmelon__/script/connections/connections.lua:179: in function 'recheck_factory'
factorissimo-2-notnotmelon/control.lua:617: in function 'recheck_nearby_connections'
factorissimo-2-notnotmelon/control.lua:669: in function <factorissimo-2-notnotmelon/control.lua:650>

picking up the building and replacing it allowed me to place the belt with no issue

Identical error on my end. My theory is this has to do with using Picker Tools to slide a factory around, so internal and external connections don't line up quite right. With OG Factorissimo 2 this would leave a sort of ghost behind and was obviously broken behavior, but probably since there's no visual issue it's not immediately obvious that this is going to cause a problem here.

I have added factory buildings to the picker dollies blacklist. Thanks for the report.