UserStatusChangedEvent causes EXC_BAD_ACCESS

## Overview
UsersStatusChangedEvent causes EXC_BAD_ACCESS when it arrives.
## How to reproduce
On test provider:
* connect User1 & User2
* as User1 register for user stats changed
* disconnect as User2
* sleep (or work) for ~1s

Happens also the other way round (as User2 register and disconnect User1)