It seems that the MySQL driver is missing, which is causing the Maintenance Mode Failed error after upgrading FusionAuth from version 1.36.0 to versions 1.41.0, 1.42.0, and 1.43.0.

Here are some suggestions to help resolve the issue:

Check the FusionAuth container and ensure that the MySQL driver is present in the classpath. If it is not, try adding it manually to the classpath or update your container image to include the driver.

Verify that the MySQL container is running and accessible. Check that the database URL, username, and password in your configuration file are correct.

Check the version of MySQL in the container and make sure it is compatible with the version of the MySQL driver being used by FusionAuth.

Try upgrading to an intermediate version of FusionAuth first. For example, upgrade to version 1.38.0 before upgrading to 1.43.0, to see if the issue persists.

If you are still having issues, check the FusionAuth support forums for similar issues or open a ticket with FusionAuth support. They may be able to provide additional guidance or assistance with resolving the issue.