Powerflarm IGC log MALF or user error?

I searched a bit and found nothing similar to this problem.

My Powerflarm IGC log function has worked fine in the past, but on my last two flights, I obtained an IGC log file with size 0 bytes and file creation date of -/-/1979

My LXNav S7 Vario is getting NEMA sentences from the Powerflarm as the S7 is using the PowerFlarm as GPS source and displaying 'arrival altitude' with the 'Get Home' function. I've not checked for the PowerFlarm icon on the S7 for the last two flights.

My guess is that I'm turning off power to the PowerFlarm too soon after landing. The manual says 'allow two minutes' after coming to a stop 'to avoid losing data' (I'm definitely losing data).

So I land, get out of the glider, wait for golf cart to arrive (probably more than 2 minutes stationary), tow glider a short distance, turn off Powerflarm immediately after the golf cart tow stops. Do I need to wait an additional 2 minutes after the golf cart tow stops before I turn PF off?

Any ideas for debugging this problem are appreciated.