It's because SR has higher traffic and a higher number of simultaneous connections.Due to the way hidden services are designed, at some point all that traffic - and all those connections - go through a bottleneck of a single, shared node that is also relaying other traffic. A node may get congested with close to 1000 to 2000 connections, or traffic can get backed up due to bandwidth demands and time out before completion. Keep in mind that 1000 connections doesn't even mean 1000 users, as each page load opens up several http connections, and Tor keeps those circuits open for 10 minutes.There are some solutions to alleviate the situation, but they are custom, complex and expensive.Give SR some time to adapt and design a more robust system; it's not going to happen overnight, but I guarantee you he is working on it.