I am running a 1.8.9 Spigot server with VanishNoPacket v3.20.1, however, when regular players use tab to auto-complete names, it includes vanished players as well.
The whole player base now knows of this bug and are using it to see if there are any vanished players online.

Is there a work-around or fix for this that does not involve disabling global tab-complete?

bungeecord, yes.
thanks tho

When you say "global" tab complete, are you talking about within a single server or some sort of multi-server setup?

If one server, we're talking about a bug in Spigot.

If multiple servers (bungeecord?) it's a bug with whatever else is providing that.

sorry! :(

I'm sure there are 1.8.9-relevant plugins for bungeecord that properly modify it. VNP sends info to bungeecord on vanish status change, and handles requests coming from bungeecord plugins. And there are other ways to not have that info be revealed, I think, though it has been a while.