You might try copying one of the shows to a USB flash drive and then play the show from there to see if it works properly. The reason to try that is to eliminate the JBOD enclosure as a part of the problem.
If I recall correctly, there were issues with some USB/SATA converters and slow speeds with the RPi4.
Okay. Are you saying copy it to a USB 3.0 flash drive or USB 2.0 drive? Does it need to be a flash drive or can it be any drive? And once it is copied do you want me to access and watch the mkv file on the PI from the flash drive? Just for clarification.
Should I also try to plug the enclosure into a USB 2.0 port instead of 3.0 to see if that fixes the issue? The enclosure is 3.0.
I also plan on trying no buffer in advancedsettings.xml when I get the chance.