That's because $address() uses the Internal Address List (IAL) to return addresses. The IAL only stores addresses for nicks which it knows the address of, which is something that cannot be guaranteed for any given nick. So you shouldn't use $address() in remote events because you cannot be sure that it will return anything. Instead you should use either the relevant identifiers as listed in /help Remote Identifiers or in the case of raws, use $1 etc. as Bekar explained.
