[arsMOBILIS]

Just updated from 5.0 to 5.1 on a Windows 10 PC and I can no longer connect to my device via USB.

5.0 connected fine then asked if I wanted to update to 5.1. I said yes and downloaded/installed it and now no USB connection.

Reverted to 5.0 and USB connection works again.

Unfortunately, I was unable to duplicate your issue.  I re-tested USB connections using Windows 10, 11, macOS and Linux and didn't run into any problems. I understand you've rolled back to 5.0, but if you'd like to investigate further you can install 5.1 alongside 5.0. Just install it into a different directory. The first thing to check would be a connection via the command-line to see what error messages are thrown.
 
http://www.jocala.com/connhelp.html

I solved my problem but I don't really know why it works this way. I had adbLink 5.0 installed in C:\Program Files and it works fine there. Version 5.1 OTOH exhibits the problem I described if installed in that directory. Moving 5.1 to a different path makes it work properly again. I know that C:\Program Files and C:\Program Files (x86) are protected by Windows, but something must have changed between 5.0 and 5.1 because the former works fine in those locations while the latter doesn't. Here's the really weird part... adbLink2 5.1 and wsaLink both work fine in either of those locations, it's just adbLink that won't.