MaxScale Loads Incomplete User Metadata Resulting in Authentication Failures and Backend Auth Errors

During Kea DHCP startup troubleshooting, authentication failures were observed through MaxScale despite valid database users and successful direct MariaDB authentication.
Investigation identified discrepancies between user metadata visible in mysql.global_priv and the user information being loaded by MaxScale.

*Observations*
MariaDB contained expected users:

SELECT COUNT FROM mysql.global_priv;

Result:

15 users

However:

SELECT COUNT FROM mysql.user;

Result:

1

And:

SELECT User,Host FROM mysql.user;

Result:

1 | 1

MaxScale logs reported:

Read 1 user@host entries from 'mariadb-0'

Authentication failures were observed:

Authentication failed for user 'kea'

A newly created test user also failed through MaxScale despite successful direct database authentication.
Additional Findings
MaxScale backend servers entered:

Auth Error

state:

mariadb-0 : Auth Error

mariadb-1 : Auth Error

mariadb-2 : Auth Error

resulting in:

Could not find valid server for target type TARGET_ALL

and application failures:

MySQLdb.OperationalError: (2013, 'Lost connection to MySQL server during query')

Troubleshooting Performed
Reviewed MariaDB and MaxScale logs.
Corrected grants for:
maxscale-server
maxscale-sync
maxscale-monitor
Recreated mariadb.sys.
Investigated mysql.user inconsistencies.
Validated MaxScale configuration and user synchronization behavior.
Worked with MariaDB Support.
Impact
Kea DHCP startup failure.
Application database connectivity failure.
MaxScale unable to properly authenticate users.
SIT2 testing blocked.
Expected Result
MaxScale should load all database users and successfully authenticate valid accounts.
Actual Result
MaxScale loads incomplete user information and backend servers enter Auth Error state, causing authentication and connectivity failures.
Requested Investigation
Validate why MaxScale only loads a subset of available users.
Investigate synchronization between mysql.global_priv and mysql.user.
Validate whether the issue is related to system schema corruption, MaxScale metadata loading, or restore activity.
Provide root cause and permanent fix.
These two defects clearly separate:
Restore-induced mariadb.sys / database corruption issue
MaxScale user sync/authentication issue
which will make tracking and RCA much easier.