In the view "list all spider activities" there is the block "Block remote TAS". This display has an "AND" and an "OR" group in the filter section. With the OR-group in place, the was no result even with simpler conditions. Searching through the issue list led to a core issue for views which finally resulted in a patch (https://www.drupal.org/files/issues/2020-10-14/2559961-101.patch). After applying this patch the view worked as expected. This needs to be checked when the upgrade to Drupal 9 should be done.
