nRF52382 low power RTC data lost
The current draw is ~80uA peaks (I think when RTC is counting),


That is probably too slow measuring equipment. The peak sould be MUCH higher, as the RTC is very simple and needs the CPU (in)frequently. The CPU core requires current in the mA range - which your coin cell cannot hope to provide.

Luckily, the current draw is rather short. A capacitor in the 100µF range across VnRF might do the trick.

Almost forgot: The NRF chip triggers POR when VCC changes more than 0.3V in a short time frame. This might bite you here, too.