As I can see from the video you've sent, the track is loading slower than playback goes. Which is obvious I guess.
It fully depends on your internet connection speed, as FLAC files are "heavy".
I suggest checking your internet connection speed with this tool https://speedof.me/ and compare your results with the FLAC files size.
So it obvious if the problem is an internet connection or not.
If your internet is a bit slower then needed for FLAC steaming, I suggest downloading your music for offline listening!