problems with some rss feeds

by marteng69, Thursday, March 02, 2017, 13:07 (2704 days ago) @ jtojnar

Replace
return $userAgent.' ('.implode('; ', $agentInfo).')';
with something like
return "Mozilla/5.0 (X11; Linux x86_64; rv:54.0) Gecko/20100101 Firefox/54.0";
(the user agent of a browser, that displays the feed correctly)

I replaced the line, but the error remains. Then I changed the FF version from 54.0 to 51.0 but it is still not working.
Any other ideas?