I had ghost modules (construction requests) on the furnaces and their beacons on 1.X version.
After the migration to 2.X version, the ghosts (most or all, I didn't pay attention) disappeared. I placed them back (copying furnaces with modules over them with a blueprint).
Most of them were constructed ...

What?
Allow fast-replacing for arithmetic and decider combinators while keeping the wires

Why ?
Arithmetic and decider combinators have the same size and the same set of outputs. Quite often you want to have different operation with the same inputs, like:

Before:
decider: A > B => output 1 C ...

There were two crashes of the same game (single player, no mods) within half an hour. I don't know what caused them and how to reproduce, so I just attach logs and dumps after the second crash and the last autosave before the second crash in case it would help.