I’m getting the same 503 error, it happened 6 times during the last 2 weeks with my two websites. It was working fine but later on it started causing error. I deactivated all plugins and tried to activate one by one. I found it is Jetpack. Why it is happening? I’m not sure if any other plugin or my theme is conflicting with it. But both websites are hosted on different servers and using the different plugins, just jetpack is same in both.
Thanks!