Would you be playing .wmv files by chance? As this is a known issue with the proprietary Microsoft format and Linux and there isn’t a fix more so a work around where you convert WMV files to either MP4 or MKV formats by either installing ffmpeg from Entware and running it on the command line to convert the files with whichever example suits you best or if your not so good with command line Linux then download and install Handbrake and use that to convert.