What would be the cause of such a drastic drop in one month?
It may be something as simple as mechanical problems on the well.
Oil wells go down from time to time for servicing. It could be worse, though. There might have been a mechanical problem in the well that caused the well to quit producing forever.
Don’t panic until you see the following month’s check.
Buddy: Happened to me, too. Seems like they shut down the well while drilling another well adjacent thereto. Back on line in a couple of weeks.