I've found an issue with the core config manager while editing with users that have limited access to the CCM. For instance, an user with this configuration can trigger the bug:

Steps to reproduce:
Add or modify a host/service to have the limited user as a contact (or via a contactgroup). In my case, PRUEBA_ALTA_IMPORTADA. A couple of minutes later, it can be seen by the user.

The issue comes while activating/deactivating the service using the limited user. Toggling the activation status using this link (marked in green) works fine, editing permissions still work:

But unselecting this checkbox (marked in red) and saving the service breaks the permissions. After that, the service can't be configured by the user anymore.


Pressing twice on the activate/deactivate link seems to fix the issue.
Specs:
CentOS Linux release 7.5.1804 (Core)
Kernel 3.10.0-229.el7.x86_64
Manual installation - Nagios XI 5.5.4 latest (was upgraded manually from 5.2.9)
Thanks,
Gonzalo