Is your mono audio like, in the middle?
Like; when you go to your iPad's settings and click Accessibility and find the Mono Audio option, is it centered? Because one of your speakers might be broken while one might not be.
I mostly think that it is a bug now. I haven't opened the HS app for a while now, so I don't know if it's a bug for some devices. (Oh; also, our iPad's speakers doesn't work... But earphones do work, so try using earphones too)