We can replicate that when 1) a user started audio playback, 2) left the app, 3) paused playback from music controls on lock screen, 4) waited more than 5 minutes (but less than 10 minutes) to resume playback, without re-entering the app any time during that period, that the playback controls appear but do not function. 

Standard native Android behavior is that player controls are cleared off the lock screen after 10 minutes. However, Android's system handles battery/memory usage for background apps for web views (which our app runs in) by freezing use of media controls at 5 minutes. This creates a five minute gap with non-functional player controls. Unfortunately, according to our developer, there is simply no good, reasonably priced way to change it given Android's limitations and the way our app is developed. So at this time, we will not be pursuing a fix for this but if there is enough user demand, we may reconsider in the future. We only have a finite number of dollars to use for app maintenance and new features.

We are actually working on a dark mode for the entire app right now, so this will be coming by end of the year or early next.

This was fixed in the October app update.