I had a very similar problem with my C1 Pro.
I first noticed an issue when I checked footage one day and noticed there was nothing recorded for the last couple of weeks. The issue seemed to start around the time I updated to version 1.9, although I can't be certain.
I formatted the microSD card and the issue seemed to disappear for a while, possibly until the card was full and the dash cam was overwriting older files. Again, I can't be certain about this.
After that I did tests in the house overnight and there were significant periods of time not being recorded. I could not work out a pattern or reason as to why those periods wouldn't be saved. I formatted again and continued to use the dash cam whilst monitoring what it recorded. Eventually it started to only save the final segment of each journey.
Throughout my issues I was in contact with Anker support who said this was a previously unreported issue and offered to send me a replacement free of charge. I'm using the replacement which is running firmware version 1.8 and I haven't had any issues so far.
This post leads me to think that it is an issue with the firmware on the dash cam rather than it being a faulty device.