The bug report (Failed Loading Plugin) 0013785: [Addon D3Charts] Descendant indented tree fails in Gramps v6 [ SyntaxError: invalid syntax ] - Gramps - Bugtracker – Free Genealogy Software was about the report failing due to typo. This typo was fixed.
I ran on gramps 6.0 and used Mac Safari and the reports displayed correctly.
This does not address the Issues listed in the Addon wiki for Firefox and Chrome.