I think there is some weighting based on how often you go to a certain result after typing a certain number of letters. For example, since I was just doing Advent of Code and going to related sites:
a, ad, adv -> first result is adventofcode.com/2023
adve -> first result is adventofcode.com/2023/day/1 [honestly, this one baffles me, but I guess I went back to day 1 at some point after typing `adve`]
adven, advent, advento -> first result is reddit.com/r/adventofcode
adventof -> back to adventofcode.com/2023
I actually *appreciate* this behavior; it means I can better muscle-memory a certain number of letters and go down to the first result when 2 sites have similar names (very annoying for twitter & twitch btw).
So I don't think the problem is that weights can change as you type more letters; but that an entry can disappear altogether when there are no other suggestions.