Thanks for the advice.
Some strange happenings since... while the tempertature setting drops to 59 on its own, it will go back up to your desired setting if you hold down a couple of the buttons... like the directional keys, and even the light key.
I was also able to get the temperature back up by holding down the temp key until I could keep it at 104, then locking the panel. It heated to 104 without resetting, but as soon as I unlock it it goes back down to 59. I can't get the pumps to work while it's locked either.
I'll check into James' suggestion of a faulty topside (not sure what that means, but I'll tell the technician), but one thing I think it could be is an overheating issue with either the heater or something else. The one time it did work normally this weekend was when I had the panels off, making me think it may be overheat related.
Anyway, thanks again for the help and I've passed it on to a technician to look at.
I'll update what the result was when he's finished.