Reproduces on v5.14 RC5, v1.22 build 221 Android
1. Make a post containing a video file (I used an .mp4)
2. Tap on the video thumbnail in the post
3. Tap on "Download" but then tap on "Cancel" (I only did this twice before the error displayed)
On cancelling the download for the 2nd time, I got an error: "Video playback failed - An error occurred while trying to play the video. > OK"
If you tap on "OK", you get an endless spinner, like the video is trying to load/play but nothing happens. Tap the "X" to exit the video preview screen and tap on the video thumbnail in the post again
because the video wasn't actually downloaded the first time after the error was displayed, you can tap "Download" to properly download the video (this works as expected).