why doesnt it locate a device, just continues to search. but never locates

on find my iphone when trying to locate all the devices set up in my family sharing it just continues to search for once particular device all the rest of the devices show up or say online not sure and location or off-line but this one particular device just continues it just says locating locating, locating etc.. is there a certain setting that someone can place on it to not show up but also not say off-line or can the phone be wrapped in tinfoil and signal blocked or what are the possible scenarios that would case this?