In most cases these issues are solved by clearing your web browser's cache and cookies or logging out and logging back in. Below are some additional trouble shooting tips that will usually solve any playback issue
a Try removing browser installed add-ons.
b Make sure that your operating system has all its important updates.
c Restart your computer and your modem
d Try another browsers, like Firefox, Google Chrome
e Make sure any browser extensions/plugins/firewall programs you may be running are not causing the problem.