Hey folks just trying to get to grips with Motion Studies and I'm somewhat stumped

I cant share my assembly as it is proprietary, however, the issue I'm facing is:

I have a fully working fully dynamic moving assembly, everything drags around well constrained etc overall I'm happy with how it's all going when I move to start a motion study I've watched several videos and think I know what I should be doing but clearly, I'm missing something!

with auto keyframing on click over to 2-seconds move a part and a perfect keyframe is created:

next step I want to animate a part starting from there, so I clicked the item created a keyframe (so it would begin as my first keyframe finishes)

next, I jog along the timeline to 3s and go to move my next part at this point the entire assembly is completely frozen and i cant move any more parts no keyframes are created and i'm stuck!:

can anyone help me untangle what's going wrong here I've tried to follow all the guidance verbatim from numerous videos and they all seem to just work .. mine, however .. just doesn't haha!! I appreciate any response on this !!

this is the tutorial I've been trying to follow along:

SolidWorks Animator Tutorial - YouTube

they key difference from his video other than I'm using SW 2018 is when the instructor clicks a new timeline location the keyframed area stays yellow, on my view id loads in red almost as if it's pre-rendering something here perhaps this is the problem ? or there is some 2018 change I'm not privy to that's tripping me up

hopefully, someone can assist I'd really love to leverage animation from SW Assemblies ASAP!

Thanks!

Luke Daley