So first results trying various encoding options in vidcoder seem to suggest that the 'variable framerate' and or quality too low setting has something to with it. Unfortunately the current version vidcoder (12.xx) crashes when using 'constant framerate'.
I now have 2 versions, one with higher quality with variable framerate where the stuttering is reduced considerably, and one with pure handbrake 1.11 'constant' framerate but higher quality (and pretty slow) that has no stuttering. So it seems this the way to go when confined to using these devices. I don't know about the other arm broadcom baesd devices, but I suspect they aren't that different there.
Normally, in vidcoder, I use constant quality settings around 20 to 22 for BDs and UHD BDs, and also keep the variable framerate setting.
When I'm done, I'll let the forum know the modified settings that I have decided to use.