my question now is, what will be happen, when I use this WBS210 with this two mentioned antenne ? It would not be able to use 2x2 MIMO if you use an omnidirectional and a directional antenna at the...

Klingt für mich mehr nach einem DHCP-Problem in Deinem Netz (zu kurze Lease-Lebensdauer) als nach einem Fimrware-Bug des EAP. Hast schon mal probiert, die Undok app zu beenden und neu zu starten nach...

The one found on the german support site for EAP225 V3, it's REV 4.3.0 December 2018. Make sure to select V3 as the hardware version on top of the support site.

Set your PC to static IP 192.168.0.10, connect to the switch using its default IP 192.168.0.1, log into the web UI, change its password, set the switch's IP to an unused one of your network...

It's documented in the EAP225 User's Guide on page 17: Guest Network: With this option enabled, guest network will block clients from reaching any private IP subnet. This is different from AP...

Did you try to reset the switch? See this FAQ on how to restore factory defaults. Does the password work after resetting it?