Wireless doorbell connection -121 error

The home base 2 lost connection with the wireless doorbell and shows a -121 error. It worked flawlessly before this problem. The doorbell is wired to supply the power and the battery was fully charged before the connection was lost.
What does a -121 error mean and how to resolve it.
The home base 2 works because the video stream from another connected eufy cam 2 is still working.

Mine does the same intermittently especially when sun shines directly into camera.Please fix