I think i know why this is happening, its being generated on the fly and has no information to blend between, but i was wondering if its something that can be solved?
Attached video of spline geo not working with retimer.
Yes if you're birthing new particles like that, there's no interpolation data for the retimer to use.
A trick you can do is: spawn and then save position using a Custom Properties operator. Then snap the particle to the parent's position with Set Target/Move Target, then interpolate back to saved position using a second Custom Properties operator.
That way there's never a point where a particle pops into space at a unique position....they are birthed on their parent and interpolate smoothly to their position.