MP4 Export File

So I have several streams I'm ingesting with the DVR and then exporting clips via the Export API calls. This all works fine the only issue I'm running into is that these MP4 files will not reliably import into premier and if they do they take really long time to import. File durations are between 5 and 60 minutes long and max size is around 3GB. Small files seem to load in fairly reliably but can take a few minutes to process larger files around 60 minutes typically take 5-10 minutes for premier to import them if it even does. My experience is that premier will typically import MP4 files regardless of size almost instantly and this is not happening. If after downloading the files I use ffmpeg and do a straight copy so it rewraps the files they instantly load into premier without issue. If anyone has run into this before and knows a fix for this or why it is happening please let known so maybe can I tweak somethings and get these files to work in premier.