Confluence has bugs that can affect rendering nested macros inside of Multiexcerpt Fast Excerpt (Block or Inline) macros
The Multiexcerpt Fast Excerpt macro will render an error message when it cannot nest another macro and the root cause is a bug in the Confluence API used by Multiexcerpt.
- The macro may be nestable if you switch to including it via a regular "Multiexcerpt Include" rather than the "Fast" variant.
- Please contact Atlassian Support (Confluence Cloud) to let them know what type of macro you tried to nest and that it cannot be rendered by vendor apps via Confluence's contentbody/convert REST API.
- Give your feedback to Atlassian about their decision to stop supporting nesting bodied macros by voting on or commenting on CONFCLOUD-68323 and the related issue CONFCLOUD-58656.