Just tested. There are 6 posts in this thread by yourself and Jon.
I added Thanks to all 6 of them (then removed them again).
So I'm not getting the same results as you for whatever reason ...
....and clearly nor did new member jocph (nor hassanogaibi who also did mass thanks about two years ago).
Perhaps Jon has added some means of blocking massed thanks recently, but, if so, it doesn't seem to affect me as it does you