Gsuite, but I presume regular gmail would have the same behavior. If it helps, mine was from pixelfed@pixelfed.sdf.org with the subject: "Confirm Email"
I'm in the same boat, I tried to login awhile back and had issues (I don't recall what they were), and attempting login today shows my creds don't work anymore.
I hadn't seen that there was an instance now so this inspired me to go check it out, thanks! I thought I had the same issue, but it turns out that the email was just getting tagged as spam seemingly because of no SPF, so DMARC fail.
The other (first?) part that has sound: https://archive.org/details/0619_Computing_For_Fun_04_01_26_00