Shulker not counting towards mobcap

In my survival world i have a peaceful mob switch similar to the one built on the scicraft server. It uses 70 shulkers trapped in the spawn chunks to prevent aggro mob spawning in the world. However, it would appear that these shulkers caught in 1.15.2 no longer count to the mobcap as monsters still spawn in the world and in the spawn chunks when the switch is on.