The next Kintone update is 7th September 2018. The release also includes the following bug fix.

• The Bulk Request API currently returns an illegal request error when the request contents are invalid and it is initiated by Guest Users.
  After the fix, a 400 Bad Request error will be returned stating that the input is missing or invalid.

Updated notice on September 5th 2018
If the Bulk Request API is used to process a long request, and the request involves operations that result in Kintone notifications being sent (for example by setting up Per Record Notifications in an App), other notifications cannot be sent on Kintone until the operation for the Bulk Request API request finishes.