Missing Dataflash Log Files - ArduCopter 3.3.3

I have had several occasions (arducopter 3.3.3) where no dataflash log file was produced during a flight (or several flights).

I have verified that the sd card is usable, get the expected beeps when copter is powered up.

I tried a very short arm, move servos a bit with RC Transmitter, disarm - and I got an SD Card (dataflash) log file. Re-installed the card and flew - with no log files produced!

It is sometimes critical to have these log files (photo tagging if automatic tagging fails!) or post flight analysis.

log bitmask set to 456703 - normally logs a lot of data.

Thanks for any suggestions / help.