/my-stuff/ is sort of a placeholder. I know it’s blank now. I was testing out woocommerce but it’s currently deactivated, but I was planning on integrating it in the future, so right now it’s just there. Nothing links to it, so I didn’t really see the harm. But it’s not necessary.
Okay. So following your advice, I got rid of my-stuff. I moved /activate and /register to No Parent, emptied the Pages trash, checked my Buddypress pages settings, and saved my Permalinks structure.
And now it works fine. Argh, the frustrating part is I don’t know what was wrong with it…