Access Denied for all sites collections in same content DB while other content DB`s Sites are ok

Question

Env: SharePoint 2016 on-prem

I have 3 content database under 1 Web Application. there is 1 content database (have 6 site collections) suddenly became "Access Denied" including sites collection administrator account but all 2 other content database is working fine...

HOWEVER, if add "Everyone" with "Full Read" in "User Policy" under" Manage web applications" all user can access anywhere in the 1 content database (have 6 site collections) .

All Database are in working mode, not "Error or Read-only" Please help

Answer 1

As mentioned in this post:All Users (Including Site Collection Admins) receiving Access Denied from one Site Collection

You could first check the web application policy to see if the superuser and super reader accounts are normal.

If missing, try to add the superuser and super reader account with permissions read and full control.

See reference: Configure object cache user accounts in SharePoint Server