Multiple players have reported a playerlike entity, sometimes with a skin and a name, flying above them. 
As there are only two active staff members, neither of which has been doing this, this must be the same bug that we experienced pre-update.

I myself have not seen it (due to permissions maybe?) but other players may be able to provide screenshots

I've seen this actually too, it seems like a plugin would be causing it (sometimes plugins create player entities to modify things such as the tab list of bossbar).  I need to look into this further, I'll get back to you on this.

This issue may be related to /vanish;

https://www.spigotmc.org/threads/major-invisible-player-glitch-afflicting-my-server.27756/

I think it is from Anti-cheat as an entity for kill-aura, a normal player won't normally hit it but a kill-aura will. This is how the detection system works. I could easily guess that an op player will never see this feature. But the downside is that the entity flys in your combat path and you hit it anyway. KICKED: Aura-like combat. Grr

Alright, I need to keep an eye on this.

@lela_null: what evidence do you have that would suggest this is from AAC?

I know a guy that cheats a lot and while testing some configurations on my server he knowticed the ghosting when I started assing different Anticheats.

How often does this issue happen and on what servers?

Survival, Creative; anytime there is any thing hapening. Swing a sword, dig, mine, build, eat.

This issue is bizarre. @lela_null: could you please keep a list of all playernames which you see appear in ghost form and whether or not they are online when the issue happens.

I saw my friend as a ghost today and he was online (far from me) and that was weird.  I will collect some names and I will also have them help me test some stuff on a private server to try to get exact combinations of the issue, including the plugin and possable configurations that might correct the issue.

I'm tired of being kicked from the server for Aura like combat.