Simple diffusion of lipid-soluble molecules through phospholipid bilayer -- does anything get "stuck" in transit?
I interpret your question to refer to the movement of a lipid-soluble molecule that is therefore able to diffuse into cells down a concentration gradient. I think that you are asking whether as the gradient collapses, some of these molecules would "stay in the bilayer".

You are thinking about the diffusion process in the wrong way. There will always be a pool of these molecules in the bilayer, and these will be continually exchanging with molecules in the two aqueous phases on either side of the membrane. The net flux which results in diffusion in any particular direction will be the  movement that results from these equilibria. Diffusion isn't a directed process in the way you define your question.



My diagram shows on the left the progress towards equilibrium and on the right the situation where it has been reached. Note that at equilibrium, because it is lipid soluble, the molecule is at a higher concentration (larger typeface) than it is in either aqueous phase. And - importantly, molecules will still be moving into and out of the bilayer at both faces.

Added later:
A classic example of a lipid soluble molecule able to diffuse in this way is oxygen. According to this paper, at physiological temperatures, and at equilibrium, the concentration of oxygen in a bilayer will be approximately 3x that in the surrounding fluids.