Apps publishing error after reassigning smart groups

[cafefii]

We added all users to a (big) smart group before and have assigned different apps to this smart group.

We split this smart group into three (small) smart groups and want to transfer/assign the apps to the three small smart groups separately(editing on the old assignment as the users should not notice the change).

Still, an error "Save failed, Please try again." was always displayed after clicking "PUBLISH".

What can be the reason for the error message, and how can we change the assignments in our use case? Or "Delete (old) assignment -> publish -> add (new) assignments to smart groups -> publish " is the only way?

Context: self-hosted Workspace ONE Version 20.11.0.17 (2011), all devices are iPads Pro 11' 2020.

[cafefii]

Some users are now using a new email service, they are using a different exchange server, so we need to change the assignments(in Boxer). I also tried (keep old assignment) add a new assignment with the new setting, whatever which priority the new assignment has (before or after the old one), it also doesn't work.

[cafefii]

workspace one support solved it.

- purchase new licenses 

- delete old assignment

- add new assignments

- publish