Great, let me know how they work for you! I hope this saves you some of the misery I went through. 😉
Yes! It turns out it’s a known issue with Learndash. That link goes to a support log-in for their FAQ, which provides a workaround. To be honest, I only found out about this after stopping using LearnDash, because the problem made the site essentially unusable. So I haven’t tested it for myself.
When BBPress is turned off, the error stops. When it is turned back on, the error starts again.
Also, the BBPress rewrite rules, especially the root rewrite stub, are the only place in the entire code base that I can find the rewrite rule RegEx fragment.
Coming back to answer my own post, in case it helps someone else down the line: the shortcode (for the individual forum ONLY) was distorted in Visual mode. Switching to Text mode and correcting the shortcode seems to have fixed the issue.
