option 'preserve children' missing while the move/rename process

This affects only some of our many users. If user want's to rename/move a page w/ children the checkbox "preserve children" is not existing but then appearing after renaming/moving in the status page. See images:

3 users had different behaviours:

• person 1: problem existing > switch to inkognito mode > problem solved > back to normal mode > problem solved
• person 2: problem existing > switch to inkognito mode > problem solved > back to normal mode > problem not solved
• person 3: problem existing > switch to inkognito mode > problem not solved > back to normal mode > problem not solved

With person 3 we tried more options but the following did not solve the problem:

• switch person 3 account to "advanced user"
• make person 3 an admin
• switch to inkognito mode
• switch browser (edge, chrome)
• switch pc (but user profile is synced from server)
• delete and recreate (automatic with oidc an azure ad) person 3 account

What suddenly "solved" it (better to say seemed to solve it): person 3 only tried to rename articles in a "special" root space w/ restricted "delete" rights. But this person is in a group having this right. After trying other articles in other root spaces (where instantly this problem didn't appear) we returned back to articles in this "special" root space. Now the problem was gone. No idea what it cured.