This has happened to some people on previous updates. First time it has happened to me. Found a chat with a resolution from 3 years ago and it still works. You need to install a driver update from Trainer Road USB drivers, and then once installed, run the exe - dpinst.exe. I then closed Garmin Express, re-opened it, and sync of my watch and recognition of ANT stick was resolved. I am a Windows user so do not know if it works for other operating systems. Link to info from 3 years ago is:
forums.garmin.com/.../affer-garmin-express-update-to-7-3-1-0-ant-stick-is-not-recognized