I'm resposting from this thread to hopefully create more attention for this problem: https://answers.microsoft.com/en-us/outlook_com/forum/outlk_win-outtop_new-outsub_ofb/outlook-error-message-someh...
Hey I also wonder if this happens if you spin up a new AVD host? That is something I'll be trying next, especially since you mentioned it's an issue even after re-creating the user's FSLogix profile. Curious to know if you made any headway on this issue?