The only other thing I can think of is clearing any missions in your journal that are tied to leveling, e.g. introduction to bases, artifacts, allies, etc.
Hmm... did you try to talk to Tala in the Hall of Legends or in the Tap Room Safe House? I wonder if the progression missions are tied into the Seasonal Events; I usually wait until I have done Constantine's artifact mission with a low level toon before using them for seasonal events and I've not had a problem getting in them.
My level is 18 by the way. Still have missions, etc. And it doesn't let me to talk to her. According to the fandom, the min. level for the event is 10 but I'm 18. Odd.
Ah, you had said you were level 20 in the first post. They raised these to that level, so that was why I thought you should have access. Events are now gated at level 20 and not level 10 (starting with Witching Hour 2021).
No worries. I understand people sometimes round up, and the combat rating vs level can also lead to similar confusions.