Try changing your sequence settings so that the:
Editing Mode is set to "Custom"
Preview files: "Quicktime"
Codec: "Apple Pro Res"
Sometimes H264 gets jittery due to the default preview settings for H264 media.
You cant "do" Apple Pro Res on a PC.(apart from edit it)
But mainly..the issue is not noticeable in my sequence or system players. Only on others (MAcs)
I just had a call from one of them that they just installed VLC Player...and the files run as they do for me. (Perfectly smooth)
Issue is not solved though if PremPro ( Mac vers) cant play and edit them.
Setting the preview files in your sequence setting is not permanent. The
Mac users can set their preview to whatever codec runs smoothly for them
and the PC users can have their own choice of codec. Or you could try
choosing the same codec for both machine that works cross-platform.
Either way, that's the first thing I'd attempt if I was troubleshooting it.