Keyframe glitch - 'ghost frame' jumps

I'm animating a very simple illustrated film using keyframes to flick between mouth positions for lip-syncing, eye movements etc. referencing frames in a sequenced asset comp via time remapping.

All works fine 90% of the time but then I get glitches in the preview where AE seems to add in a keyframe one frame before a real one resulting in a flicker to a random space within the asset comp just before the true movement I am aiming for.

I have tried:

Frame rate - ensuring the asset comp and main project have matching rates.

Interpolation - is set to hold as it is a simple 'stop motion' effect so no linear interpolation or easy ease in place.

Rendering - some of these glitches disappear when the project is rendered but some are not and occasionally new ones appear which I have to go back to fix before re-rendering.

The only current fix I have is to create a new layer in the asset comp then reference the new frame in the timeline but this is a bit of a bodge and is time consuming when I have to repeat multiple times in a project.

I've seen other people have this problem online but never found a solution.

It's driving me crazy!

Thanks,

N