Welcome to our forum @AndrewK! In this case there could be a couple of reasons. One of the properties of guest wifi is that the connection is simply slower. This could be the reason. Another property is that the device connected with the guest wifi can not make connections to other computers that are connected to the same modem. I must admit I do not know enough about Roblox to know if this is something the game needs in order to function. Do you happen to know if this is the case?

Hi @AndrewK! Seeing as we've not heard back I`m going under the assumption that the problem has been fixed. Because of this I`m closing the topic. If there's any other questions on the subject you can put them here and we can see what we can do still.