The reason is that basically. when you have a container that have NH4OH in it, you basically don’t have ammonium ions NH4+ and OH- ions as we are used to, instead, you have NH3 and some water in there because ammonium hydroxide is not very stable to stay that way, that is why those NH3 molecules will react with AgCl to make a complex of Ag(NH3)2+ with some Cl- ions as byproducts, this is also not a very stable products, and it will revert back to initial reactants (AgCl) and ammonia will be given off as gas