I have some old TV shows that play jerky on Roku -- but not on Android or on a PC (using Emby in a browser). The files are already mpeg4 format and play without transcoding. They were originally recorded using WMC using an old HDHR tuner, and I likely used MCEbuddy to re-encode them. They are only around 2 Mbps so it is not a bandwidth issue. Furthermore, back when they were originally recorded/re-encoded I swear they played back fine on Roku (with MediaBrowser running WMC server).
I have attached a log file that includes me playing first on Roku and then on my PC. I have tried playing on an Express+ and Primere (both wifi) as well as a Roku 3 (wired ethernet) and get the same results on all three.