[need help] Converted mp4 file makes trouble with PPCC17

so...

i had a *.mkv file and converted it with ffmpeg to a *mp4

with this comand "ffmpeg -i FILENAME.mkv -codec copy FILENAME.mp4"

that worked.

Now always if i import the file into Adobe Premiere Pro CC 2017 the timeline moves if i cick play but the preview window doesn't move at at all or just minutes later (and windows says my CPU perfomance goes up to 99%).

i am fairly new to Adobe Premiere Pro tbh.

my Premere Pro

the file i am working with after converting

my quite bad rig but i dont think that is the problem bcause i also edited longer 1080p files with it without problems

error i got yesterday trying to edit this file but not today

i hope u can help me