For those of you who were having issues connecting to the Forums, it turns out that our modem was not functioning properly. We have replaced it now and the connection to the Forums has been restored. Thank you for your patience.
The stopping does not appear at any given specific time. It will stop at random moments. I do hear that when it stops there is sometimes an audible pause in the beating (which will sometime resume on its own, sometimes not).
You might also have one hooked or otherwise malformed tooth on the escape wheel. In your pic, I think I can see one hooked tooth at the bottom. Look at each tooth on the EW and see if the end is bent over or broken.