Hi @Tioz. This looks to be due to some Sphinx updates. It is a very recent error that only just started happening in the master build a couple days ago, and has been fixed in https://github.com/nengo/nengo/pull/1623 (not yet merged). Specifically see the commit titled “Add docstrings to WeakKeyIDDictionary”. You could do a git fetch && git cherry-pick c92678f12361673170cacf9842a36565eb553c1a (at time of writing this) if you wish to pull this commit into your branch.