AFAIK, rendering/displaying a note in Obsidian is done “on demand” (not sure if it’s the right term 
and also if it works this way on both desktop and mobile 
) …
In other words, when you scroll while in Live Preview (I’m not sure about Reading or Source 
), what kind of happens is that Live Preview gets the raw markdown content from Source, reads/parses it to finally render/display it the way it should look like… and as it’s done “on demand”, this only happens for a portion of a note…
This means that the whole note isn’t pre-rendered in case you might need it when you scroll but it’s rendered “bits by bits” while doing so 
… which can become a bit problematic (depending on how long the note is, how much the parser needs to work, how fast you scroll, your device, maybe other things I don’t know about 
…).
On mobile (iOS/iPadOS), I’ve personally run into this bug: Bug: Scrolling long notes, scroll abruptly stops in between (at least once, on a somewhat long list … I’ve haven’t checked that note in a while though) but I have no idea if you might be facing the same issue though …