WordPressMU Problem with EDIT Links

Another Problem I with my WordPress MU Setup ( about 20 pages) since last update to 5.03 and switching to the Classic Editor:

On all Sites / Pages, the EDIT Button is broken as you can see here:
https://<pageurl>/wp-admin/post.php?post=7&action=edit

it should be:
https://<pageurl>/wp-admin/post.php?post=7&action=edit

I am getting crazy about that, I disabled many plugins, tried different themes and so on – it happens on all MU Sites regardless of used plugins and themes.

Any help would be appreceated.

• This topic was modified 7 years, 4 months ago by Steven Stern (sterndata).