[acdha]

> It can take a second or so for letters to echo until the keyboard code warms up its cache, or whatever it’s doing immediately after it is displayed.

This is rare but it also goes back to the earliest iOS releases. Once background apps became possible swapping became common, especially since most people just enable it for every app which asks.

> I’ve also noticed that I sometimes have to click the fingerprint sensor 4-5 times to get the pin screen to display.

This also sounds like memory pressure. It doesn’t happen normally even old older hardware.