Steps to reproduce:
1. Update Q&A to v126.96.36.199
2. Save permalinks in admin
3. Go to a user or edit page. For edit pages I get 404 and for user pages, it lists all questions and doesnt show a specific user (it displays the page for user=NULL because it cant find user=matches1).
I tracked this down to qa/core/core.php, line 288. esc_url_raw() removes square brackets and so index.php?qa_edit=$matches becomes index.php?qa_edit=$matches1 and there is no question with slug = 'matches1'.
To fix, I removed the call to esc_url_raw() and then saved permalinks.