Thanks for the feedback.
I think you've both hit on something with the lack of stabilized flight mode (i.e. flight mode configuration issue). I'd missed that before but its rather obvious from the log now that it's been pointed out. You can see I was able to manually change altitude in altitude hold mode though so I still don't understand the 'floor'.
The weird barometric altitude leaped out at me as well, but it was so far off the GPS altitude that I have no idea how to interpret the mismatch.
FW should have been latest stable as of mid-November (flashed with QGroundControl around then, but I don't have an exact date).
Props were matched and had been used on prior flights. I need to absorb the rest of this info further, but in the meantime I appreciate the help.