Users connection lost

Hi,

We encoutered a serious issue in shared services authentication level.

Since 2 days some users lost access to their applications.

Symptoms:

- Some users  lost their connexion cubes

- Some of users disapeared from users list in EAS but we can find them in shared service

- Concerned users didn't get list of their cube when he connect via SmartView

- Concerned users try connecting to an application , he got error message Essbase error code 1051025:

Cannot open cube view. Essbase error(1051025): User X is not permitted to access application Y

Environnement :

Essbase 11.1.2.3 (500) on Unix AIX 7.4.1

AD used is MSAD for AD external authentication

How could I check if this is an AD issue? (file logs, specific item message, config, diagnostics,...)