guessing, but could you be invoking zsh in such a way occasionally that it is not reading your .zshrc? sudo or su come to mind..... this is what got me in bash

guessing, but could you be invoking zsh in such a way occasionally that it is not reading your .zshrc? sudo or su come to mind..... this is what got me in bash a few times - exiting a shell that had just the wrong ssettings so it ioverwrote my history.