Thanks for the update!
We can’t see any errors or issues coming from the antivirus software, so there has been no progress on our end. We currently think that a software update they pushed in September or early October is causing the problems, but there is no way for us to troubleshoot that.
For what it’s worth, AVG/Avast (and third-party antivirus software in general) have a long history of causing problems with USB devices, including MIDI.
If you are in touch with someone on their support team, please see if they can contact us at email@example.com. We have a test setup that can reproduce the issue and would be happy to work with them to work out what’s going on; until we hear an actual answer we can’t tell you why their software is suddenly causing problems.
In the meantime you can to rest assured that the antivirus software that comes with your OS (Windows Defender), if properly configured, will protect your computer without breaking your devices.