Don't ask me how I did it (because I don't actually know!!) a Zimo MX623R chip lost ALL settings - everything was showing 0 (zero) even CV 7 and 8. I tried resetting with CV8=8 several times and always it failed.
Luckily I found this page https://www.1001-digital.de/pages/programmierung/zimo-decoder/hard-reset.php which is for a HARD RESET with this sequence on entries
CV 7 = 0
CV 31 = 0
CV 32 = 0
CV 8 = 8
CV 15 = 0
CV 16 = 0
CV 8 = 8
CV 144 = 0