A calendar feed that seems frozen is nearly always your calendar app's refresh schedule, not Rennt — Google Calendar refreshes subscribed feeds on its own timetable, often taking several hours (sometimes up to a day).

First, confirm the feed itself is fine#

In Settings, use Copy URL to grab your feed link and open it in a browser tab. If a calendar file downloads (or text starting with BEGIN:VCALENDAR appears), the feed is alive and current — the delay is entirely on the calendar app's side.

Google Calendar#

There is no force-refresh button for URL-subscribed calendars, and the refresh interval is measured in hours. If you need it sooner: remove the subscribed calendar and re-add it From URL — re-adding pulls fresh data immediately.

Apple Calendar#

On a Mac, the subscription has a refresh setting (get info on the calendar) — set it to refresh more often. On iPhone, subscribed calendars also poll periodically; re-adding forces a fresh pull.

If the feed URL itself errors#

If you clicked Reset link at some point, every previously added subscription died with the old URL — that is exactly what reset is for. Copy URL again and re-subscribe with the new link.