Volumio does not open though it is visible in the network

I installed Volumio on a raspberry B2 last week together with a hifiberry digi+.

No problems at the beginning, very good sound quality. This week I tried again to connect to the UI, but nothing happened. Reinstalled Volumio, nothing. However, I can see Volumio in the Network and via wlan, but neither IP nor Volumio.local works. Interestingly, I cannot connect to Volumio via WLAN with volumio/volumio2 Login /PW combination.
I installed ropieee on the same Raspberry (since I use roon, too) without any problems. Does anyone has an idea?

Thanks a lot