A7RV - Movie file error. Cannot play back.

I was doing some photos and videos yesterday and I have noticed that once the video simply stopped on me, I had to start recording again. Later when I was reviewing what I did I noticed that on several movies I got an error: "Movie file error. Cannot play back."
This happened towards the end of the movie, it played most or all of it and then shows the error. When I view those files on computer (using VLC), it plays most of it too and then when the progress bar is at around 90 or 95% - it stops playing, progresses the progress bar to the end and finishes playback.

I am using new Lexar Professional 2000X SC Card (V90, 256GB).


Have any of you had such problem? Do you know what may be happening here? I was doing some movies before, never had this problem before. Can it be the card?

How can I diagnose the problem?

The video that stopped on me was corrupted but so were 3 others that looked like everything was all right while filming. The stop seemed completely random. I was shooting on one card only, was planning to buy another, same card, but first, I would like to know those cards are reliable and I won't get the same problem because of them.
I also realized that before I was always shooting on Lexar 64GB, that was in slot one and only recently I filled that up and the camera switched to the big one in slot 2. Those were the first movies done on that card. So.. maybe that is the potential source of problems?

You are right, I need to switch battery, format card and start testing videos on that one. Let's see what happens. Thanks for your input! :)