I've been suffering from this for a while now, and today decided that I should report. Basically, the issue is described here:

One thing that really annoys me though is that z looses its history when I press Enter rapidly multiple times (I sometimes clear my window this way), before zsh is able to prepare another prompt. This is 100% reproducible on my home machine, but not on my work machine. I don't know whether the culprit is z, fzf wrapper or zsh async, I'm just mentioning it here as zsh async may be related (I'm not sure).

And the following comment:

I've experienced the same issue with z. It's definitely a bug/race-condition in z. My theory is that one instance of z manages to read the database at some point where it's being replaced by another instance, resulting in an empty db.

For this reason I made sure that zsh-async does not run any hooks inside the worker (async.zsh#L75-L80).

I believe this issue was aggravated by either 4a8b741 or 1a361f6 or both.

@rupa Could you please look into this?