My German provider Vodafone did send me a new router "Vodafone Station"

The RE450 was perfectly fine with my old router "Vodafone Connext Box"

I saw that RE450 is not WLAN ax capable, so I deactivated WLAN ax in the new router. Still every 2-3 hours the RE450 is losing connection and has to be rebooted. What else can I try? How can I check the firmware version of the RE450? Tether App doesn't show anything about that.

I already tried using a second device which shows the same behavior.