In any case, I have found it to be a good habit to save the part any time I make a change I want to keep (Merlin’s guide is excellent in relation to how parts work by the way).
Just to see if it works- try saving the part itself.
The other possible question that came to mind is- were the samples you had loaded in the flex machines from recorder buffers? If they were (i.e. you had recorded the samples in your session then used them in the flex machines) you have to make sure you save the sample because the recorder buffer gets wiped when you turn off the OT (another painful learning experience!).
Also worth double checking that the slider hasn’t budged over a little bit, which can wreak havoc if you have different scenes loaded on A and B.
Can you check what happens if you turn the related LFO depth to zero and then trigger the slice?