@Capybara All three issues have been fixed in v2.0.0-beta.8:
Blocking profile messages no longer hides the page for yourself - The "Disable profile messages" toggle now only hides the page from other users and guests. You can still view your own profile messages page.
Default profile view now works - Enabling "Show Profile Messages as default profile view" will correctly redirect visitors to your messages tab when they visit your profile.
Reply deletion now works without errors - Replies can be deleted normally. This was caused by a query scope that was incorrectly filtering out replies when processing delete requests.
Update with:
composer update ralkage/flarum-ext-profile-messages
php flarum cache:clear