I upgraded today from Ubuntu 16.04 to Ubuntu 17.04 because my Guest Mode on 16.04 was first giving no internet connection and then later shutting me out from the Guest Mode.
Ubuntu 17.04 provides no Guest Mode, so I searched and experimented with the answers to these:
Ubuntu 17.04: manually generate guest account
Guest session stopped working on Ubuntu 16.10 and 17.04
Both give me a Guest Mode but cosmetically only on accounts screen because once I click and go into Guest Mode, I cannot go inside Guest Mode to use it - screen goes blank and then shows the accounts screen again.
I am having to use an alternative to Guest Mode by going to User Accounts in main account, and creating calendar date username, example "username-calendar_date" and then deleting it after use.