This has been a persistent issue for me as well, whether the post is public or a message. Like @hellekin I also have higher privileges on my forum (but mod, not admin).
The only liked-by users who do show up are other moderators/admin. But I’ve noticed it’s usually just one, so if 3 mods liked it, sometimes only one icon will appear and all the others say “unknown/deleted user” when you hover over the icon. Not consistent though…
The issue does not occur when logged out.
