Archive via task not possible (Notice: unserialize(): Error at offset)

If i try to start the archive task via cron or ur, i get the following errors:

Notice:  unserialize(): Error at offset 0 of 22 bytes in core/Common.phon line <b>271</b><br /> ERROR CoreAdminHome[2019-07-16 07:17:56 UTC] [7acc4] Empty or invalid response 'Authorisation Required' for website id 1, Time elapsed: 0.385s, skipping

I use Matomo 3.10 and PHP 7.2

I saw there was an issue fixed in 3.9.1, but i still got the errors. Any hints, where to search for the error?