I also use the AC-56U wireless adapter on my USBridge, it has been pretty much rock solid up until this week when I ran the update to the latest DietPi. I have also had the same issue as you twice since the update, my Router ASUS RT-AC88U can see the the USBridge and appears to be connected properly but Roon cannot see the USBridge as a networked device in the audio settings.
My USBridge is left on 24/7 and I have seen this happen before, it’s usually been after a re-boot and I have got over the issue by pulling the AC-56U out of the USB socket and plugging it back in. We had a power cut during the night when it last happened and I had to re-boot.
I’ll keep an eye on this, if it happens again I think we will have to get @Dan_Knight to look into it.