That's what I did what you suggested in your Edit.
I was looking for the option since Sync was supposedly updated to handle v0.19 and a handful of instances were already on that for weeks now. Never found the option. I just hoped a fix will come until my main instance is upgraded.
But anyway, the main thing I can use it with this workaround.
It's the same for me. I've already cleared the cache in FF and for Jerboa too. Tried to log out and log in. Tried to turn off and on the feature again to no avail. It's the same on all of the instances where I have registration and migrated to 0.19.
A lot of things. But specifically this week it's the Lemmy v0.19 upgrade. I'm going through the github release, the various posts on the various instances, gathering every info I can find.
You are not doing anything wrong. She is a bitch.