SUMMARY


STEPS TO REPRODUCE
1. Download video and audio files from android phone and test them (they all play as expected)
2. Transfer files from phone to PC using KDE Connect by remotely browsing the phone storage withing the Dolphin File Manager.
3. Files arrive successfully. Try and play the received media files.

OBSERVED RESULT

Almost all the files don't play. Only one or two will play. For audios, a few will only play the first few seconds (less than 10 seconds) and exit with error codes.
I tried playing the received files using MPV, VLC, Gnome Videos, Haruna. They all failed. 
Sending the files back to the android device and trying to play them withing the android device results in errors also (they no longer play in the android device). I am not sure whether its the android KDE Connect or the desktop KDE Connect causing this.


EXPECTED RESULT


Operating System: Arch Linux
KDE Plasma Version: 5.21.5
KDE Frameworks Version: 5.81.0
Qt Version: 5.15.2
Kernel Version: 5.12.1-zen2-1-zen
OS Type: 64-bit
Graphics Platform: X11
Processors: 4 × Intel® Core™ i5-4200M CPU @ 2.50GHz
Memory: 11.1 GiB of RAM
Graphics Processor: Mesa DRI Intel® HD Graphics 4600

ADDITIONAL INFORMATION

I wrote that um using Arch Linux but this problem has presented itself in two of my other OS installations, namely Ubuntu 21.04 and OpenSuse Leap 15.2 . At first I thought it was OpenSUSE, then i tried in the other two distros and my files were corrupted in all cases.

In dolphin and nautilus, the corrupted files don't show thumbnails.