Update - Atlassian have confirmed that the issue is caused by their new editor, and have provided the following statement:

"Many 3rd party apps (that is, macros that have been downloaded from the Marketplace) are experiencing additional bugs in the new editing experience. We are working on fixing these, and have avoided rolling the experience out to new pages for the sites affected. "

https://confluence.atlassian.com/confcloud/confluence-editing-improvements-945107733.html#ConfluenceEditingImprovements-Reportabug

Unfortunately, there is no action that affected 3rd party apps such as ours can take to mitigate these bugs, and we are relying fully on Atlassian to address these issues.

We will continue to leave this incident open until Atlassian have confirmed that a fix is in place.
Mar 19, 09:34 AEDT

Update - We are continuing to await further information from Atlassian regarding the issue concerning the new Confluence editor.

Most Cloud instances already use the new editor for blog pages and meeting notes, so even if your instance has not yet been upgraded to the new editor, you may still be affected if you attempt to place one of these macros on a blog page.
Feb 19, 15:28 AEDT

Update - We are continuing to await further information from Atlassian regarding the issue concerning the new Confluence editor
Feb 19, 12:08 AEDT

Investigating - Atlassian are progressively rolling out a new editor experience for Confluence Cloud (https://developer.atlassian.com/blog/2018/12/new-year-brings-new-confluence-cloud-editor/).

We have had reports from some customers in the initial set of Confluence Cloud instances to have received the new editor, that many 3rd party macros (including ours) no longer display correctly, and instead show the message "[confluenceUnsupportedBlock]" in place of the macro.

We have confirmed this to be a problem with the new editor, and have reported the issues back to Atlassian.

Atlassian are actively working on a range of issues affecting the new editor, and we hope that they will have a fix for the problem as soon as possible.
Feb 19, 09:00 AEDT