Doorbell Duo not detecting all motion events

My Doorbell Duo cam is not detecting all motion videos. I have an SD card, so I can see all the missed events and all the incomplete videos. Most of the time, the videos are only 9 seconds long, even though I can confirm with the SD card recording that there is motion for longer than the 9 seconds. In some other cases, there are plain missed events, where the SD card recording has obvious motion and no event is recorded/generated.

I’ve tried changing the sensitivity and event settings, to no avail. I also have the latest firmware. The only thing I’m doing which might be affecting things is that the camera is mounted sideways, as I wanted to use the second camera to cover a blind spot next to my door.