When going to a Dashboard in Portal web UI we see the following message about "Page <number> not available".
For example using a bookmark to access the ACI Reporting->ACI Switches Overview OOTB Dashboard the following is seen.
The number in the message, the internal unique (one per Dashboard) PageID that represents the Dashboard, will be different for each Dashboard.
All supported DX NetOps Performance Management releases
The Dashboard is not part of a Menu the User has access to.
Determine the Role used by impacted Users.
Edit the Role and add the Menu that contains the necessary Dashboard to allow the user access.