After migrating from 12.2 to 12.3, log entries of previous task executions can no longer be viewed.
The problem is due to tasks that were performed before the migration.
When the tasks are run again under 12.3 U1, this error no longer occurs when navigating to the new flows, and the log entries are displayed normally again.
You can also run the following SQL query to regain access to the old log entries:
UPDATE [TaskHistory] SET [LogAvailable] = 0 WHERE [LogAvailable] IS NULL