I'm not kidding you. They DDoS themselves because the app apparently doesn't cache anything.
Oh, and don't try what happens when skype.com doesn't work. The whole app goes maniac then.
Also, I believe those re-authentications are actually ALL the app is doing in those moments.
It's not actually loading anything, not emojis, not notifications or anything else (all of the app still works normally) - it's just re-authenticating, re-authenticating, re-authenticating, re-authenticating... in the background (eating quite a bit of CPU and bandwidth in the process).
Why people still do that?
When I ran a very large O365 environment, it was even harder as we had a dedicated 10Gb circuit to Microsofts network, and and depending on various bugs, conditions, etc, you could easily send traffic to the wrong place and impact performance. (For example, if you inspect TLS traffic, that latency will kill Outlook application performance)
A few times I got into a weird auth bug scenario, where if a window popped up to auth, and I didn't get it right the first time, it would send me into an endless loop of popping out auth windows (while Teams shows me offline). Whether I succeed with auth in the subsequent windows or not, or even whether i just dismiss the window, it doesn't matter. They kept popping up almost instantly again, dragging away window focus from whatever other application window was in focus. Even closing Teams wouldn't help, only reboot would reliably resolve it (though given how few times I've observed it, I didn't bother looking deeper than that into it). And that was on macOS.
The other big issue is that they saddled with the technical debt of legacy auth, and many failure scenarios lead to that path, which really sucks.
It usually works fine for an hour or two after restarting the app - and then it suddenly starts refreshing endlessly as fast as it can.
There's no visible reason why it would suddenly be doing so many API requests, and wasn't doing them before. (And then stops doing them again, after being restarted.)
I only figured it out by accident - through the Microsoft Authenticator App I got to a login/authentication history somewhere, and there I saw that Teams was automatically re-authenticating itself in the background. Probably some sort of token renewal or something.
But it was doing that LOTS. Like 2 or 3 times per SECOND. And once it starts doing that, it seems to be doing that indefinitely (until you restart the app) - with absolutely no hint of what's happening inside the app.