why do some videos recorded open and close--not playing

1. Some videos, not necessarily long on you tube --like 1 out of 10 open and close in 5 seconds --never having recorded although there is no way to know this happened until I try to look at them.

2. Why do some videos not play well--they skip spots leaving missing words, visual jerks. No warning that I need to re-record.

Is it because I am on satellite and service gets slow toward the end of my time period? (After the new period starts, then I get fast downloads for a week of so. Then it gradually slows down.)

I am enjoying using 4K--my first month.