I get the "not enough space in chest" red error when the crafting combinator is trying to switch recipes.
The overflow chest options seem to do nothing - even with different chest types or directions.
I have a few mods active, but nothing that changes the chests.

This can be fixed by ticking the "discard items" box, but wastes a lot of resources.
Hopefully you can get the overflow chests working.

Works fine for me with a plain old steel chest... Do you have any more specific steps to reproduce? Also, which version was this in?

Factorio 0.18.47 (build 54412)
Mod version 0.15.3

I'll try uninstalling all other mods and see if it works.

Still happens with only "Crafting Combinator" and "Creative Mode."

Crafting combinator is on write. Steel chest behind assembler (opposite side).
Discard items unticked. Discard fluid ticked. Empty inserters ticked.

Manually change from one recipe to another using a constant combinator linked to crafting combinator with red wire.

Still has "not enough space in chest" red error floating above the crafting combinator.
The inserters feeding the assembler keep filling and the assembler keeps producing initial recipe. (as items in assembler cant switch,
If I pause inserters so items empty, it will then switch recipe without issue.

Seems like an amazing mod otherwise mate! Good work on it.

Sorry for the late reply, I missed the notifications somehow...
i'm not sure if you figured it out already or not, but from your description, it sounds like you're putting the chest in the wrong spot. Behind means behind the combinator, not the assembler - the three options for chest position correspond to the three possible spots around the combinator with the hypothetical "front" being where the assembler is.

Thanks, fixed. I was putting it on the far side (behind) the assembler.