Current sphinx build of HTML has numerous warnings - duplicate labels, underlines that are too short, docs that aren't in any toc tree, undefined labels.
Just throwing in an idea, the GeoTools doc build actually fails when those warning show up, the GeoServer one does not. I'm not sure if it's a good idea to suggest to make it more strict, or not, but could be matter of discussion on the ml
First, make it not fail...
Mass closing all resolved issues not modified in the last 4 weeks