I have the same issue. I’ve been in contact with Customer Support for that reason for quite a few days.
On day one of owning the H90, the unit was connected to the Control App with no issues. When I disconnected them, I plugged the MC-6 Pro to change the bank layout and returned to H90; after, it refused to link. I have removed the H90 from the app to add it again, but that didn’t work. I have done several things, including Windows restore to the time before I started having connection issues (Windows 11 Home edition), Reinstalled the H90 app several times, updated Windows twice, restarted the computer more times than I can remember, disabled the VPN, the AntiVirus, any apps or hardware using the USB connection. Nothing works. Funny enough, the Control App on my son’s computer works just fine. My H90 has the latest software, and the Control app is the newest. I don’t know what else I could do. I thought of posting here asking for anyone’s ideas, but I’m still in contact with Jerome, who is trying his best. I know the issue is with the developers, who previously stated that another device or software claims the USB, hence the connection issue. But I don’t use any other USB stuff, no DAW or anything else.