Sorting of content elements in page module

In TYPO3 10.4.1 the sorting of content elements in page module is sometimes not right:

When adding a new element between two others or when dragging an element to a position between two others, the element is placed corrctly but then the page reloads and the element is placed somewhere else.

• I have a mix of default content elements (text, textpic) and gridelements containers.
• I have fluid based page module enabled but same problem without.
• I have allowed/disallowed settings in backend layouts an gridelements. With them in fluid based page module, drag&drop is not possible at all. Without them in fluid based page module the error discribed below occurs.

Environment:

• TYPO3 10.4.1
• PHP 7.3.14-1~deb10u1