Survey map panel plot missing on readthedocs

I just noticed that the survey map panel plot [here](https://gammapy.readthedocs.org/en/latest/image/plotting.html#multi-panel-galactic-plane-survey-image-plots) is missing on readthedocs.

It works for me locally, so probably something doesn't work properly on readthedocs (e.g. APLPy or ???).