The guest account not really a guest account, it has attached to your phone by IMEI (or other number)
If it's an Android emulator, change everything (imei, serials, mac etc) if you can. If it's your mobile phone then it's ****ed, create a fake fb profile if you want try out hacks.
(Also if you want to log in to other fb account, you have to wipe cache, because it's saving it... Not enough to switch user in FB app)