And just when you think things are about to get worse…they get better. On a lark I went in and re-saved the Permalinks configuration on my site, and the Sitemaps appeared again. It looks like it is working.
So a word to the wise, if you ever update BuddyPress and use WordPress SEO, be sure to check whether your sitemap is still working, whether the BuddyPress page titles are working, etc. If not, try and save your Permalink configuration (under Dashboard->Settings->Permalinks).
There must be a major new incompatibility between BuddyPress 2.2.x and Yoast WordPress SEO (plugin version 1.7.3.1) that REALLY needs to get fixed.
Disabling WordPress SEO is not the solution to this problem. I will have to roll back my BuddyPress installation, which is a big pain the *ss. Not happy.