I can reproduce the freeze/hang. It does eventually recover, but it will then freeze again. The issue is caused by the bass tabs in the lyrics. They cause the chord detector to freak out. Detecting chords usually takes a couple of milliseconds. With these bass tabs it needs multiple seconds to parse a single tab line (particularly those with a "5" in it). I guess it is a bug in Apples Regular Expression engine as the same code with the same input works fine in a Javascript Regex engine.
This is a serious bug caused by the nashville number system change and I will have to release a bugfix or remove the nashville feature as soon as possible.