There were a few reports that players cannot join due to missing slot amounts.
The problem is this can be happening due to tons of different reasons.

Before reporting this as a bug, make sure that you've worked off this checklist:

• You are the host
• You properly installed the mod [ Text Guide | Video ]
  • You got the latest BETA branch from Stardew Valley installed
  • You installed the latest BETA Version of SMAPI
  • When you start the game as host, it actually says in the console (!) that the playerlimit was set to
    the configured amount
• You have enough cabins (remember, each player requires an own cabin)
• You allowed Stardew Valley to access the internet in your firewall(s)

Note to myself

The slot (farmhand) list is actually generated based on the amount of cabins.

• The server iterates through each cabin it can find on the farm.
• Each cabin has an instance of NetRef<Farmer> attached to it in which all information about the farmhand is stored (and saved). This instance is appended to a list ( List<NetRef<Farmer>> )
• The list is then iterated again to get information about the farmhand out of the savefile
  • If for some reason this doesn't work, an empty farmer is returned with no info for host [ Critical Issue ]
• List is sent as memoryStream [ Another Issue can be happening here, connection related ]

No longer happens