Stripping metadata sometimes doubles video, the second half of (doubled) video is without sound
This is the Gyan's solution, and it works:

ffmpeg -ignore_editlist 1 -i input.mp4 -map_metadata -1 -c copy output.mp4


The important part here is the -ignore_editlist 1 option  (yet undocumented).



The reason is that the original video contains for its video stream an edit list (elst box) with entryCount value set to 2 (which is ignored by some media players — but not by FFmpeg, which interprets it as repeating the video stream twice).

The Gyan's explanation (see ticket #8456):


  The video stream in this file has an edit list that says that the video should be displayed twice. So actually looping the video is the correct behavior. But I think the file is actually invalid, as the duration of the track in the tkhd and the mdhd box both shows 6s, although it is double that after applying the edit list.




Note:
 I tried several videos converted by Any Video Converter into the H.264 format (as input files), and the same problem occurred with most of them.