What I'll suggest may not be considered scientific, but in my case it worked.
Pull the OVP out. Make sure the flap is closed and holding the flap closed, shake the OVP. If you hear any rattling, something has come loose inside and the device is faulty.
I read about this technique here and also had it recommended to be by an MB tech - local independent shop.
Some part of the internals had apparently come loose as I heard rattling when I shook it. My problem was stalling after restarting a warm engine after sitting for 20-30 mins.
Replaced OVP; it hasn't reoccurred since. That last stall was about 2 months ago. My issue may not be related to the original posters, but the infamous OVP was brought into the conversation.
See Steve Brotherton's remarks in this thread:
an OVP question