Thousands.

Alone from a few people around me and myself are 1,2k+ autojoiner report tickets pending, since year(s).

The dumbest autojoiners, a few hundreds, activate on top the, integrated, thanks script that write a "thx" message in each GA they enter.
You have them here too in the comments but i am not allowed to name them or i would get punished harder as they (sadly no joke).

Maybe interesting for you:
https://www.steamgifts.com/stats/community/support
https://www.steamgifts.com/stats/community/active-users

You are able to check your winners with https://www.sgtools.info/activation
If something red appears then request a reroll, copy the sgtools link of that user into the ticket, and the mods handle the rest and give you instructions if you need to do something.

The result with such checks are EXTREME when you deactivate the automatic sending of the keys in a 50 copies+ GA because some people, with a lot of unactivated wins, enter prefered the 50+ copies GAs because nearly none of the gifters send them manual or check the winners.
Do it 1x and it will open your eyes :o)