With the Join/Leave notifications enabled on the most recent open beta build of the VRChat Client, joining any instance will now spam you with join notifications of other players who are already in a given instance. This is something that does not happen on the live build.

This might not seem like something that is very impactful in an instance that has maybe a small handful of people, but imagine a much fuller instance of anywhere between 50-80, or even a bumped up instance of close to 100 users then you could see how this gets a bit spammy fairly quick, especially with what appears to be one notification a second.

The same occurs when you leave an instance, so you get leave notifications from an instance that you are no longer in, in addition to the batch of join notifications from the instance you have just joined as described above.