Crawler stops after a while

The last time I updated the device was a year ago. I didn’t want to do any updates, because I was happy with the performance of the device. I don’t remember the version of the firmware. If you want, I can find it in logs or somewhere else.

Old firmware

I added some photos (~500)  and after 3-4 days I noticed that none of them was crawled. Until then I didn’t had similar problem.

New firmware

I updated the device to the latest firmware and I did a rebuild of the database. Since then I have the behavior I described in my previous post.

Is there a way to find why crawler stops or/and force the crawler to continue?