Section 3.10.4 (UNSUBSCRIBE Actions) does not define the actions to take when the subscription is a shared sub.
At the very least this needs a reference to section 4.8.2 (Shared Subscriptions) but should have some text here.
The 0x00 (Success) return code for UNSUBACK needs to be clarified. Saying the subscription is deleted is at best ambiguous in the case of a shared subscription.
There should be another return code to indicate whether the subscription still exists given that this session is no longer attached to the shared subscription. That is, was this the last session attached to the shared sub.