Sending PlayersFailedToConnect for 4 players

[furiousV]

Hi,

Occasionally on my MvM server, I get the following repeatedly on the server console:

Sending PlayersFailedToConnect for 4 players:
    [U:1:xxxxxxxxx]
    [U:1:xxxxxxxxx]
    [U:1:xxxxxxxxx]
    [U:1:xxxxxxxxx]

The xxxxxxxxx being Steam IDs which I've masked.

Sometimes it's 5 players or 6 players, and the corresponding amount of Steam IDs.

This repeats every 1 second, and the Steam IDs do not change. I presume there is a group of people trying to connect to my server and not getting anywhere until they give up?

Googling the above yields absolutely no results.

Has anyone else encountered this?

Cheers.