I have 2 RCA brand and 1 LaView brand. All three are being used. One RCA and one LaView experienced offline issue about a week ago, but the other RCA never had any offline issue at all. Weird. I viewed all three on the same phone app. Anyway the offline issue I suspected was the server from Hikvision lost communication to the phone application. But the
doorbell itself did not lose connection to the server and thus motion alerts were still triggered and sent to your phone but the app was showing offline.
I always just go to either the web portal or IVMS 4200 app to reboot the camera. Then do manual adding on the phone app using the the 9 digit Serial number. The 9 digit serial number on some brand does not appear on the sticker of the doorbell camera. My Laview one does not have the 9 digit serial number but a very long S/N with numbers and characters mixed. I had to mark down the 9 digit serial number when I scan the QR code. The RCA brand does have the 9 digit serial number on the sticker.
Once finish manually adding serial number, wait for it to indicate online or offline. Keep trying until the doorbell comes online, then type the 6 letter verification code on the sticker. Then you can quickly add the camera back to the phone app.