[Image link fixed] That definitely looks like a hardware fault. Either a faulty switch, or board, or an internal connection.
Definitely - if sold as fully working, it isn't.
I'll suggest again, try and get a more user-friendly (and less aged) mixer. Even if you have to pay more, you're unlikely to regret it.
No doubt in my mind that it's faulty.
And, remember, he'd done a reset before the original post, so there's been a lot of rather pointless dancing around here.
You're a masochist!
These desks were great in their day. But a 20 year old design with a dreadful interface, and no easy remote control (I can't count Studio Manager) really doesn't cut it today. Even Yamaha's legendary build quality can't beat Father Time.