During RE upgrade, overload on device failed. ISIS high metric does not seem to get applied to drain traffic between the devices . The behavior is expected and working as designed .
Known behavior , as documented in the feature set doc . Working as designed ,
https://www.juniper.net/documentation/us/en/software/junos/cli-reference/topics/ref/statement/overload-edit-protocols-ospf.html
timeout seconds—(Optional) Number of seconds at which the overloading is reset. If no timeout interval is specified, the routing device remains in overload state until the overload statement is deleted or a timeout is set.
timeout seconds
overload
The timeout is configured with a prefix-limit. If the number of prefixes exceeds the configured limit, the overload state is reached. The routing device remains in the overload state even though the prefixes have been reduced under the limit. Therefore, you need to clear the overload state using the clear (ospf | ospf3) overload command.