interesting. i wonder if nbforager changed login name around mid February?
here’s another thread that described something similar: https://forum.inaturalist.org/t/errors-discrepancies-in-getting-results-from-api-identifications-identifiers/19051 . if you look at the user mentioned in that thread, you can see a similar problem when doing a user id vs login observation search:
https://api.inaturalist.org/v1/observations?user_id=abigstone (1130 records)
https://api.inaturalist.org/v1/observations?user_login=abigstone (489 records)
https://api.inaturalist.org/v1/observations?user_login=aastone (641 records)