Today we are migrating push-notifications.nextcloud.com to a new server. In case you notice related entries in your nextcloud.log be assured that it is only temporary. The time window starts now but we don’t know any end time, especially since it involves a DNS change.
Push notifications for mobile devices are not working during the downtime. But they will be visible in the web and app when going to the notification section and also the email about missed notifications will be sent by your Nextcloud server as usual.