Camera app sometimes not saving videos

REPRODUCIBILITY (% or how often): rare
BUILD ID = OS VERSION (Settings > About product):
HARDWARE (XA2, X10, X10 II, …): X10 II
REGRESSION: (compared to previous public release: Yes, No, ?): unknown

DESCRIPTION: I recorded two short videos (less than a minute) using the built-in Camera app. Later I went to look into the Gallery/Videos but they were not there. I tried to record video several times, and none of the recordings were saved. I rebooted the phone. First recording did save Ok. Second did not. Couple of more and now it seems to work everytime, but something did happen and I lost two videos that I would’ve liked to keep.

Plenty of free space (both system and user storage).