I'm running the latest P3D version, no compatibility modes active, sim did not crash.
The wrong compatibility settings which are set by Windows are NOT visible, unless you edit the registry.
Everything worked perfectly the previous months, I have never had problems with GXS until today's update. But I noticed after closing the sim, the process "couatl64_P3D.exe" keeps running. Could that be a hint?
Couatl64_P3D.exe closes normally here and, nothing in the latest update could possibly change anything related to that. If the simulator itself crashes for other reasons, it's possible it might have Couatl not closing automatically, because if the Simconnect communication with the sim is interrupted abruptly, that's likely to happen.
First, try to wait a bit if the Couatl64_P3D.exe closes itself automatically, since it DOES have a safety mechanism that should kick in when the sim crashes for other reason and should be able to close itself, perhaps taking a bit longer.
If it really doesn't close, just terminate it with the Task Manager and see if it works on the next restart. That would be another explanation why it was "fixed" by the Live Updater, because another thing the updater does, is to be sure Couatl it's not running when you start the update.