Nextcloud Talk receives messages hours later

I sent some messages over a Nextcloud Group. The day later, I asked my wife, if she hadn’t received these messages. And they really didn’t arrive. Then I sent a test message to her account (not the group) and some minutes later she got the test message and the group messages from the day before!
On the server side the cron job is and was still ok! How could this happen?

You mean the push notification on the phone?
It sadly might be caused by energy saving settings of Android or Google while handling the push notification itself.
Check talk-android/ at master · nextcloud/talk-android · GitHub for some details

Ok, thank you.