The list of damage source resistances for custom armor is outdated: it at least doesn't contain sonic boom, and might miss more. A complete list can be found at https://hub.spigotmc.org/javadocs/spigot/org/bukkit/event/entity/EntityDamageEvent.DamageCause.html

It looks like the list of damage sources was up-to-date, but many were hidden because of stupid UI layout. This will be fixed in KCI 12.9