I have noticed that since installing this mod, some blueprints are no longer created completely. For example, tags that are added by mods are missing.
Would it be possible that your code reacts to events that change newly created blueprints?
e.g w/ your mod installed :

on_player_setup_blueprint(event)
mapping = event.mapping.get()

´mapping´ is always empty.

deinstalling you mod and ´mapping´ is correctly filled.

Yes this mod modifies blueprints, and after the update to Space Age, a lot of things that were previously reliable became buggy.

I can try to take a look at what's happening to blueprint tags when I have some free time.

I tried making a tentative fix for blueprint tags being dropped with release 2.3.13

If you're still seeing issues, please let me know what mod to test against. None of the mods that I tried seem to interact with tags much, if at all, so this is new ground for me.

Kux-SlimInserter uses tags to store additional information that cannot be stored in the inserter itself
Especially Double Inserter have to use tags for the placement of blueprints

Thanks for the tips, I'll check those out soon