System.LimitException: Too many async calls created: 2

We ran into this issue with Summer 16 and have opened a ticket with Salesforce. They acknowledge the issue is happening due to release and their R&D team is working on it.

I'm going to ask whether my sandbox can be rolled back until they fix it, which will hopefully be soon. No idea whether they can do that, though.

It looks like this is a known issue with Summer '16, and they say they have a fix scheduled for Summer '16 Patch 6.0. I wasn't able to find an ETA for the patch. Here is the issue on the Success Community: https://success.salesforce.com/issues_view?id=a1p3A0000017ysTQAQ