Machine works as expected with initial quality levels that share names with Vanilla. But when it comes to new qualities, it does not function.

I have noticed this with "Ultimate Quality" mod. It adds a "normal+", "uncommon+" etc between main groups and several qualities on top. Normal, Uncommon, Rare, Epic and Legendary items upgrade to their + variants as expected. However, the + variants do not upgrade to the next "tier" (so Normal+ remains itself instead of upgrading to Uncommon), same for fully custom qualities.

While probably not intended behavior, I'm not sure if it's possible to fix (perhaps you have to refer to quality names individually to make it function).

could you read https://mods.factorio.com/mod/upcycler/discussion/679cdc52f188d8d69ff57f0b and check if your situation is similar?

my mod does not have any quality names hardcoded so the problem basically just has to come from other mods.

if you feel like the linked discussion does not apply to you please send me your world so i can check for myself.

Thank you for the answer. I didn't think to look at your previous mod.
Yeah, that seems related. I tried with other mods - ones that don't change rarity unlock tech - and it works as advertised.
I'll try asking on their side.