Hi guys, What are the reasons why an engine's gateway might resta

This depends on the situation. If you saw the gateway restart only 2 or 3 times and it has been OK since, then that means there was a problem with the gateway and that it was able to recover from it. A restart of the engines will clear any ERROR messages.

If you are running multiple gateways then this indicates there was a race condition during the checkpoint and gw2 was able to recover from it by an automatic restart.

If you are seeing the gateways continuously restart then that could indicate a more serious issue.