[Bug]: Cannot change a sub-circles level to moderator in contacts

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

After adding a circle (of which I am part of) to another circle (which I own), I cannot change the level of that circle to e.g. Moderator. A pop-up appears with the message "Could not change the member level to Moderator".

When I refresh the page afterwards, I cannot make any changes to the circle anymore. It says that I am still the owner, but all settings are gone and I also cannot delete the circle. When I click on "leave circle" next to the sub-circle of which I am also part of, then I can leave the circle and it is gone from my list. After some time it reappears with me as an owner again and no other members. Then the situation is kind of reset, as if I would have just created the circle from scratch. I can change all settings again.

It seems to me like a bug and not a feature.

Steps to reproduce

1. Go to the Contacts page.
2. Create a Circle 'Circle A'.
3. Create a Circle 'Circle B'.
4. Add 'Circle A' to 'Circle B' as a new member.
5. Change the level of 'Circle A' in 'Circle B' to e.g. Moderator.
6. The error appears, refresh the page.
7. The settings are gone. Leave the group through the button next to 'Circle A'.
8. 'Circle B' is gone. After some time, it reappears.
9. Click on 'Circle B'. All settings should be back.

Expected behavior

'Circle A' would be promoted to Moderator.

Installation method

No response

Operating system

Debian/Ubuntu

PHP engine version

No response

Web server

No response

Database engine version

No response

Is this bug present after an update or on a fresh install?

No response

Are you using the Nextcloud Server Encryption module?

No response

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

Unfortunately I cannot tell much about the Configuration, as the nextcloud instance is managed by our faculty at the university.

List of activated Apps

Unfortunately I cannot tell much about the Apps, as the nextcloud instance is managed by our faculty at the university.

Nextcloud Signing status

No response

Nextcloud Logs

No response

Additional info

No response

Start by reproducing the issue from the Contacts page using the listed Circle A and Circle B steps, focusing on the member-level change and the subsequent circle state. No files, tests, logs, or entry points are identified in the report. Done means Circle A can be promoted to Moderator and Circle B retains its settings after refresh.