I am running into the same problem and have been unable to find any information on this error. Push notifications work properly on an Android device from the same server. Blue Iris 5.2.9.22
No. My issue was due to a third party firewall program blocking the connection to Apple and preventing push notifications all together.
I have intermittent problems with pictures showing on the notifications for both Android and Apple devices. From other threads I have seen it was recommended to use version 5.2.6.5. I tried that and it seemed to work but I was unable to playback recordings properly via the apps.
Oh okay i'll dig thru my main firewall logs then, I'm running PF sense. Yesterday I did get a couple of pictures. Is there a explination somewhere on how the push notifications work? It's a little black box to me.