Access denied on Sharepoint admin center but user has SP admin role

Obviously this issue has been resolved for user. But i had a similar experience and thought it worthwhile to post my resolution IF it helps anyone in the future,

Scenario: Global Admin creates new user from Admin center + Grants SP Admin Role.
SP Admin able to log in use all office (E3 user). Sees Admin center and OneDrive and SP Admin centers, Clicking on it gives user 'Access denied'.

Tried all below
1. Waiting 24 hours > No change
2. Removed and re-added user with same permissions > Same as above
3. EVERYTHING short of bumping SP Admin to Global Admin > Same as above.

Finally in my frustration I chanced upon the Azure AD. Nothing diff. All permissions reflected whatever Admin center showed. Just on a whim I decided to strip the admin of permissions and re-grant the SP Admin role.
WORKED!!!!
No logic but I said to myself IF anyone EVER complains - I'm doing this heading to AAD and changing permissions.

No documentation anywhere. Not even a mention of possibility exists of a sync issue - So EXTREMELY frustrating (not to mention the ... hmmm wait 24 hours and try again.) Think Users or for that matter management would like to hear that from Admins .... smh
Just for the record I had only had a default (onmicrosoft) domain

Just hope this helps someone