Hi Matt,I am Pete, and I'll be happy to assist with your question today.
The TV may be indexing the files if there are a lot of them.
Can you do a test by copying one of the files which doesn't fully play onto a separate memory stick, and then plug it directly into the TV and let me know if it works on its own?--------------------Kindly rate my service 5 stars at the top of your question page if my answer worked so I am rewarded for my time; tips appreciated :)Otherwise please reply back if you need further assistance.Pete.--------------------
Ok, where did you get the MP4 files from?
"MP4" is just a file container, the video within is likely H.264 of which there are various sub-sets of that specification like base/main/high.The Panasonic media player software on your TV is not a particularly robust media player and the files you have could have been encoded in a manner that it will not play back fully as they have some mix of H.264 profiles the TV does not support.
You could try using conversion software on your computer to convert the movie files again into a compatible MP4 format.
Let me know how it works out..