Poly TC8 is stuck on a search for updates

[sltdvg]

Devices:
Poly G7500 (OS: 4.4.2-434042; App: 6.4.0 (6657) )
Poly TC8 (Maybe OS: 6.4.2-7000764; App: 6.4.0.3448 )

Behaviour:
The Poly TC8 is now stuck at searching for upgrades after booting. I did a reset on the TC8 itself, but it still is stuck.
The ZDM doesn't recognize it as online or connected though it is connected and has full internet access, as well as access to the G7500 over the same network.
It does not search for an update if it's offline. That's the only point where I can reset it completely or can enter it's settings at all.

What happened before:
The devices failed to upgrade, which I then started manually with https://us02web.zoom.us/location to upgrade to the latest version.
It started to upgrade after removing it from the room and connecting it back to it.

What I expect:
The update to work or the TC8 to stop searching for the upgrade after reboot.

What I think:
Either it's bricked or needs a manual downgrade  to another app or OS version to accept the upgrade and run it fully.