The bug in Google Search Console's Discover performance report displayed a blue notice prompt with a mysterious hashtag and options 'Learn more' and 'Got it.' This issue arose unexpectedly.
If you have a national domain .pl (we checked .com and .net - the error doesn't occur there), create a subdomain with a name consisting of EXACTLY 5 characters (e.g., test1.jakubsawa.pl), add it to GSC (either as a property or domain), and add a link to sitemap.xml. GSC WON'T FETCH IT!