I have been having recurring issues with Teams on my iPhone 13 Pro. the phone has the latest updates and has been happening though an OS update or two so I don't think it's just my particular iOS version.
Teams opens and connects. However, many times a day, messages will be stuck on "sending". I will also get notifications of incoming messages twice. Usually, they are abut 30-60 seconds apart.If I turn off WIFI the messages send and the app works normally.
This happens on many wifi networks. When teams is not working things like slack, mail, etc are all fine. I can open a network app and ping the internet.
I have clear the data and even re-installed the app. It would not even update after signing back in unless I was off wifi.
I do have IPV6 on most of the connections. Other apps work just fine. The desktop client seems to work just fine most of the time.