Yes, I've also observed issues with minibuffer messages appearing at the
wrong place. Vertico uses overlays to display the candidate count and
the candidate list, similar to Icomplete. Icomplete however removes the
overlay in the pre-command-hook and puts the overlay back in the
post-command-hook. I am not doing that. I just move the overlay to the
end but it seems this solution is not good enough. Since I have not yet
understood fully what the problem is I haven't done anything yet to fix
the issue.