We are aware of a regression in 31.00 that occurs if you make calls to GetPlayspace from within the block of a class or a class constructor of a creative_device subtype. You may cause a crash when the device runs this code when opening the level, or dragging-and-dropping the creative device into the level. You may also encounter problems when attempting to publish the island, since it will fail the cook process. This will be fixed in a future release of UEFN.
In the meantime, you can remove any such calls within block or class constructor functions as a workaround. You may have to do so before opening your project.