Interesting that you should be having exactly the same problem as I !
I have been using this metronome very frequently and have found it much more interesting than my own one purchased several years ago.
About two weeks ago I went to use it and it behaved exactly as yours is behaving now, why I have no idea! I wish I could help you and rectify my own problem at the sametime.
I have emailed GuitarTricks with this problem but they haven't been able to help. Surely this must have become a common problem for loads of us, it certainly doesn't sound like a problem that has suddenly occured with our software.