Appium 2.0.0-beta.61 refresh API unaccomplish

I use python to interactive with appium server. But it crashed when using driver.refresh(), and appium server side show

[debug] [W3C] Matched W3C error code ‘unknown command’ to UnknownCommandError
[HTTP] ← POST /session/7bcad9ff-c231-4262-9fa7-46c7ed0ec804/refresh 404 9 ms - 3530