Voice chat hasn’t worked on Xbox for many years. It is very inconsistent.

These are the things people in my guilds do to trick Xbox ESO into working.
"Devs hate it! One-SIMPLE-trick-for-ESO Clickbait-Style" (That's a joke, mods)

Sometimes if you press "A" to enter the chat, exit the menu screen for 5-10 seconds, and return you'll be able to actually enter chat. Additionally, you can try entering into other guild channels, waiting a few seconds, then back to the one you want.

Usually Works Eventually Method Starting an Xbox party with yourself, then manually swapping to "Game Chat" with the view button also sometimes works to force ESO to recognize voice channels exist. If it does work, you can leave the party. Sometimes it takes multiple tries switching between game and party chat (give ESO a few seconds to catch up) but it eventually will work. I know you mentioned limited time, so this solution probably isn't great when you have people waiting on you.

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You mention IT so maybe you'll have some insight- how are there so many problems in Xbox like this where you can eventually get it to work just by brute repetition? Like, if it is broken, shouldn't it never work? And if it's working, why do we have to develop ways to trick the code into playing nice?

Also thinking about the login issues people with older XBoxes are plagued with, that have yet to be acknowledged by an dev or customer service rep. Thread here with links to 10+ examples that have not been solved. https://forums.elderscrollsonline.com/en/discussion/606535/xbox-login-issues-ignored-for-months-needs-dev-attention-pc-ps-comrades-plz-read

ZOS_Bill

This is getting worse day by day during this event. Yesterday I couldn't join any "all members" chat for any of my 5 guilds. I played most of the day and it felt like I was playing alone. Every member of my guild reported the same. Eventually at night things started working again (I assume as players were logging off). This is clearly a case of servers that aren't keeping up with the load and too many people allowed in each instance of Cyrodiil. Either that or you have major bugs that need fixing. I hope the server hardware replacement proceeds soon for console as it is years overdue. Hopefully there are people there actively looking into why voice chat works only sporadically. It defeats the purpose of having an "online" game when half the time I can't speak with my guild while we trying to run a group around Blackreach Cyrodiil.

Other issues during this event:

1. Heard from about 50-players that people can barely fire skills. I use a bow and when I cast Poison Arrow my bow points up in the air for 3-5 seconds and eventually the skill fires (I think). Bow skills are firing so slowly and animation is just horribly slow or barely playing so I can't even tell what's happening in combat. My kills have gone down by about 75% because I can't fire skills quickly enough to kill anyone, especially since Nightblades using a bow have been nerfed into the ground over the past 2-years as it is. I have an Xbox Series X and half-gig wired fiber internet and the issue is not on my side. It's so bad that the only attack I can do with a bow reliably is light attack and even that is slow. Imagine chasing around tanky fast players trying to kill them with weak light attacks from a bow! That is what you've reduced gameplay to for this event because of horrible performance. I've been playing for years and this is the same every event.

2. I have been completely kicked from server and crashed to desktop at least 4-times per day since the event started. Again, too many people playing and your systems aren't keeping up. This never happened even once per day until the event. (Heard this also for 10s of players on Xbox NA all weekend.)

3. Queue yesterday was 100+. People have to wait an hour just to play. Is this the best ZOS can offer your paying customers? Really?!