From what I've been experiencing based on observation with these errors that I came across some consistency, and I really do believe it is something do with this expansion.

1) I get 90006 errors out of a Primal's arse whenever I was in Zone 5, and less so in Zone 4. Zone 1-3 seem oddly fine for whatever reason, and the Endwalker dungeons seem to have this problem too.
2) Whenever I'm outside of EW everything seems completely fine.
3) I hardly get errors though if I do my Duty Finders inside of a Inn (why this happens I have no idea) except for PVP matches.

This is all just guessing work that maybe EW areas is unstable besides the congestion? Idk, its just weird things I noticed.