Alerts not loading on two from six cameras


I am having issues with push alerts on two of my cameras.
They are recorded, but I am unable to see them in the preview. I need to access to the camera and then I have to search them on the timeline to see the recorded alarms.
All cameras have the latest software.
IOS is also up to date including the app.
I tried already to reset the cameras and to reinstall the app.
Unfortunately no success.
Enclosed a screenshot of the failure code I receive.

Btw: The two cameras are the oldest once I have, I bought them in 2018.