I use EWS PushNotification to sync calendar events, but get
"Unable to retrieve events for this subscription. The subscription must be recreated., The events couldn't be read"
error after some time
Does anyone know what condition will trigger this error on EWS side?
Seems Microsoft doesn't document this...
The most common reason is the Mailbox moving which in Office365 can happen quite a bit as they patch and update servers or for load-balancing etc. This is a little old but still relevant https://blogs.msdn.microsoft.com/exchangedev/2008/07/24/transitioning-to-exchange-web-services-notifications/