There's a known issue where a device that was set to Guest Mode goes into the Guest Space after updating to Mylio Photos v24. You can solve this by going into a different device that is not locked and remotely changing the Guest Device. Here are the necessary steps:
Open Mylio Photos on another device that's not in the Guest Space.
Click on Spaces in the Left Sidebar and select Manage Spaces.
Create a new master PIN when prompted.
Use that PIN to unlock the device in the Guest Space.