Optical flows: from FCPX to Motion

Hello

In my FCPX project I have 3 clips with some speedup retiming (variable speed + speed transitions), using Optical Flow

After exporting the color grader says he sees jittery footage, e.g missing frames

I thought I'd try from Motion to see if I get the exact same results. I'm using Automatic Duck and the project translates well, but I can't see the Optical Flow option in the properties of the clips, where it should be offered.

Am I missing something ? Shall I remove speed transitions ?

Thank you for your help

In the retiming section of the inspector under the frame blending sub menu ...
hope that helps

Thank you. That's what I don't understand, it's not there (see attached)

I am quite sorry about that, sometimes ...... happens, I mostly use regular and standard codecs, so I don't know what can cause that.