I'm getting no notifications; just the message "Failed to retrieve notifications".
Looking at the call to /admin/notifications.json/task:getNotifications, the response contains an empty array of notifications:
{"status":"success","notifications":[],"need_update":true}
I do see the notifications occasionally, but most times it fails.
Are you behind a proxy server or firewall? Do the GPM updates and Blog updates work in the dashboard?
Not proxy, but I am behind a firewall. Yes the updates and blog updates always work, but the notifications used to fail almost always. But today they seem to work, maybe the problem has passed.

No, still happening; in Firefox. Not in Chrome... Weird.
I have no idea why this happens, sometimes it works; sometimes it doesn't...
Definitely sounds like a local network issue then
I use Firefox both at work and at home, but at work it's behind a proxy. Is the notification results cached somehow?
Had the same problem, turned out to be the Privacy Badger Firefox-extension blocking getgrav.org by default. 🤦♂️ Unblock and it's fixed.
Dashboard-feed is crawled by the webserver. Dashboard-notifications by client. I am right?
I think both should be done by the webserver to avoid cross-origin errors.
@Rotzbua Yup, that's correct. I've got an error on the notifications because of CORS for a while now :D
I'm actually already working on this. Newsfeeds and Notifications are getting a little refactor that should make them faster and more reliable.