I saw in the changelog that you deleted solo play in the zombies menu, and i understand why you did it, but there are some things that change when playing custom games. For example, when playing solo Mob of the dead you have 3 afterlifes, and in cg no matter how many players there are, you always have 1 afterlife max. Or the power up that you get from the first chest in Origins.
I don't know how you can fix this without having to add the solo play button again, maybe making a command that lets you change the settings of the game, or making that every cg with only one player has solo settings.
@Koswen This is fixed in an upcoming update. Games will function like a solo match if the min players option is set to 1(default), or a coop match if the value is greater than 1. You can still invite your friends mid game in either case so you can play MoTD with solo rules if desired.