Scores frequently won't play

As a piano learner I use the website (only) to read and play scores in the public domain and frequently for no apparent reason a score - any score at a given time - won't play at all. This seems to occur randomly - in any browser I use at that particular time - regardless of logging on and off, rebooting the entire laptop, deleting cache and cookies; nothing works. Until suddenly later on, everything works fine.

What's up with this? It's really frustrating to have a subscription and to find that randomly no scores of any kind on the website will actually play.