Render image api does not work with parity report plugin

The render api (
http://<USER>:<PASS>@<HOST>:<PORT>/render/dashboard/db/test) seems to produce a 504 error when including a parity report panel in the dashboard(
This functionality works with the same dashboard when the panel has been removed. With the panel added, the identical api call subsequently fails with a 504.

Is this normal?

Many thanks

Are there any suggestions for alternatie solutions?