When you have been cruising for 30 minutes or more, and you need to stop and shut off the engine:
When restarting the engine from 5 minutes to maybe 30 minutes after shutdown, you run the risk of heat soak.
To minimize the effects of heat soak (what I believe to be your issue), after the restart, run the engine at a high idle (1500 RPM for 15 seconds) then at a higher than normal idle (1000 RPM for another minute) BEFORE continuing your journey. I think you will find the issue disappears.
Jon
