eDLT failure and replacement issues

I've had one of my eDLTs fail, screen went blank, appears on the network, buttons do nothing. Connected the USB to try to reflash the firmware, but is not shown to exist.

First question, is there a process to have eDLTs repaired?

So I dig out another eDLT which went back in its box 7 years ago when we have some house remodelling done. I copied the failed unit's config to a template and then loaded that template to the replacement eDLT - but it's not responding well to button presses. Looks OK, but you have to repeatedly tape a button for it to action, and even more to turn a light back off.

Next I tried a factory reset, started anew, and just tried manually setting button 1 to turn on a light. Same issue.
I then moved the eDLT to another location in case there was a wiring issue, same problem where there is a working eDLT. So wiring discounted

I've run the CBUS diags tool, it's scanned the entire network and no errors coming up with everything classed as 'perfect'. I had upgrade to firmware 18, I've now downgraded to 17 but the issue persists.

I've had this system in for 22 years, and this is the first issue I've ever had!

Thanks