Unique permission issues with group members disappeared from document libraries acl

Hello

we have a big issue on a project teams. The item is a Teams with the associated SharePoint site. What is happening is that suddenly members couldn't access anymore to many folders and subfolders in Teams (and as well in SharePoint) while owners could still work fine.

What we did to investigate is to check permissions understanding that there were a lot of unique permissions active and we have broken the unique permission through a script. After a while that all the libraries where correctly settled inheriting the permissions from the parent site the problem showed up once again: many folders and subfolders with unique permissions present...

To preserve business continuity of the project we are running more times in a day the script but we don't think it could be a valid solution...

To have more control on the site for now there is only a site owner and the sharing content option has been disabled for everyone except the owner. I add that on the impacted folders the group member is automatically removed every times that unique permissions appears while the owners and visitors remain active. Deleting the unique permission automatically restore the member group and all the team users start to work again on the impacted content. Any idea?

From the audit log we have found that defender for cloud app has removed the external sharing on some files where no activity was made, but this should impact only the external users not the members... I appreciate any help, we are getting mad!