When user cache flush occurs ?

[sc]

Dear all,

We get a wierd issue yesterday that without touching anything all our user was not able to loggin anymore to jira using their AD accounts.

We notice from user management that user was not anymore belonging to groups even groups was really there.

I have heard that this can happen if a user cache flush occurs in background

But then I have a stupid question :

1 - When this user cache flush is trigger ?

2 - Who decide to trigger the cache flush ?

3 - What happen if an AD sync occurs at same time user cache flush is in progress ? I guess strange unstable thing

Does anyone have any answer to those questions ?

Regards