@Lexenos Hi. The loop checkbox is only enabled for APNG file types, it doesn’t weigh in for video files, but just to try that out, simply select the APNG filetype when using the [Browse] button. Then uncheck the “loop” checkbox, go back and change the filetype to MP4 and report back.
I personally think the problem here might be actually that you’re using a non standard resolution, which is neither 4:3 nor 16:9 which MP4 H264 codecs sometimes have trouble rendering (and VLC / WMP might have trouble playing too, though this is rare). Also the pixel aspect ratio might be affected by the strange resolution as well.
Just to test the latter please change your camera layer size to 960 x 540 (just NOT change the export size on the window options or else your file will become distorted) and try to export the MP4 again.
If it works let us know as well as this could be investigated as a bug. If it doesn’t work them please upload your PCLX file to wetransfer.com or google drive and share us an anonymous link so we can test the file export. I have Windows 10 so it should be a similar environment.