H80, One of the digital coax inputs stopped working

It's possible you have a bad solder joint on the coax input that quit working or a connecting wire may have come off.

Welcome to the forum.

Not sure what the issue could be, a bit surprised you're having an issue with Hegel. I assume when you say the other input worked you used the same cable? If anything digital begins to act up the first thing I do is make sure it's not the cable.