Essentially, sliders snap to the final tick it can reach, and the length is decided by how far the slider can travel between the start and end tick.
When total distance which the slider produced by the nodes you have drawn is less than the distance it can travel between two adjacent ticks, the slider becomes invisible, since it snaps the end tick to the starting tick, i.e. it travels for 0 seconds and thus it has 0 distance.
When the nodes of your slider make a slider long enough to fit between 2 adjacent ticks at the current slider velocity, increasing the slider velocity without increasing the length of the slider means that the required distance for two adjacent ticks is increased, and so it is possible that the slider no longer reaches the next tick and instead snaps the end tick to the same tick as the starting tick, in which case the situation above occurs where the slider has 0 length.
This is why your slider disappears, It was a bit wordy and I'm a bit late to this but I hope it helps.