A recent upgrade to your JIRA Cloud instance has introduced some incompatibilities. Atlassian is aware of the issue. To avoid these issues, you should upgrade your client to the latest SNAPSHOT for release 5.1 available from Release Notes 5.1.
This release of the JIRA client includes some new implementations using the latest JIRA REST APIs. While we strive to maintain upward compatibility of the interfaces, some incompatibilities may appear. More details are available in JIRA Jira 7.0 Support Notice.