trust_level_0 is the default value for uploaded_avatars_allowed_groups.
Everyone is in tl0, as you expected.
WIthout looking at commits, my guess is that there is or, more likely, was, a bug and that an upgrade will fix it.
That is how it’s supposed to work.
You might share your exact commit and maybe look at titles of commits just before ((and maybe after) that.
I edited the subject to maybe get more attention if this is a bug.