I use AE for animating, and I use the slider control a lot. What I'll do is make a precomp with mouths that i've drawn, for example, and then I'll add the slider control and time remapping to the precomp so that I can use hold keyframes to switch between frames in the precomp and lip sync in this case. (This video explains basically my exact process in a couple minutes: https://www.youtube.com/watch?v=lZ7KgavJZ20) The problem is, it just bugs out sometimes and it's such a pain. Sometimes a frame will decide to display every frame at once (sometimes without a keyframe on that frame, and I use hold keyframes so there should be absolutely no change on that frame whatsoever), and sometimes it changes frames not on the actual keyframe, but too early or late. In one project I fixed that by shifting everything in the timeline over a couple frames. One time I went from 10 on the slider to 0 two frames later, and it forced a 5 (i think) in the middle frame. I found that it simply will not allow me to jump from 10 to 0 without adding something in the middle.
I'm not sure if any of this makes sense, but it's just seemingly glitchy and messing up in completely random ways. Is there something I'm overlooking with this, or is the slider just a glitchy piece of trash (or maybe just not meant for this intense of use? but that's a poor excuse imo)
In theory, I don't see a problem with your workflow. Hold keyframes should keep the value constant until another keyframe is encountered. I suppose it wouldn't be a keyframe interpolation problem because if that got set to something other than hold, your keyframe shape/icon would change and you would notice it. To narrow down the problem, what if you use regular keyframes and see if you still get glitching? For example, set a keyframe for the value of 10 where needed, and then the frame before you want to change to 0, set a keyframe for 10, and then set the next frame to be the value you want (0). This is essentially making a hold out of non-hold keyframes. If you still glitch here, maybe there is value looking into clearing your cache or updating?