今天 appium 执行 iOS 用例突然报错，蛋疼，wda-test 正常，先 mark 下问题，有没有大神遇到过的？
appium 日志如下：

[JSONWP Proxy] Proxying [GET /wda/screen] to [GET http://localhost:8100/session/451C2C3C-EAC5-4D67-8D97-8057A857F08C/wda/screen] with no body
[JSONWP Proxy] Got response with status 200: "{\n  \"value\" : \"Unhandled endpoint: \\/session\\/451C2C3C-EAC5-4D67-8D97-8057A857F08C\\/wda\\/screen -- http:\\/\\/localhost:8100\\/ with parameters {\\n    wildcards =     (\\n        \\\"session\\/451C2C3C-EAC5-4D67-8D97-8057A857F08C\\/wda\\/screen\\\"\\n    );\\n}\",\n  \"sessionId\" : \"451C2C3C-EAC5-4D67-8D97-8057A857F08C\",\n  \"status\" : 1\n}"
[MJSONWP] Matched JSONWP error code 1 to UnknownError
[MJSONWP] Encountered internal error running command: UnknownError: An unknown server-side error occurred while processing the command. Original error: Unhandled endpoint: /session/451C2C3C-EAC5-4D67-8D97-8057A857F08C/wda/screen -- http://localhost:8100/ with parameters {
[MJSONWP]     wildcards =     (
[MJSONWP]         "session/451C2C3C-EAC5-4D67-8D97-8057A857F08C/wda/screen"
[MJSONWP]     );
[MJSONWP] }
[MJSONWP]     at errorFromMJSONWPStatusCode (/Applications/Appium.app/Contents/Resources/app/node_modules/appium/node_modules/appium-base-driver/lib/protocol/errors.js:789:10)
[MJSONWP]     at ProxyRequestError.getActualError (/Applications/Appium.app/Contents/Resources/app/node_modules/appium/node_modules/appium-base-driver/lib/protocol/errors.js:683:14)
[MJSONWP]     at JWProxy.command$ (/Applications/Appium.app/Contents/Resources/app/node_modules/appium/node_modules/appium-base-driver/lib/jsonwp-proxy/proxy.js:236:19)
[MJSONWP]     at tryCatch (/Applications/Appium.app/Contents/Resources/app/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:67:40)
[MJSONWP]     at GeneratorFunctionPrototype.invoke [as _invoke] (/Applications/Appium.app/Contents/Resources/app/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:315:22)
[MJSONWP]     at GeneratorFunctionPrototype.prototype.(anonymous function) [as throw] (/Applications/Appium.app/Contents/Resources/app/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:100:21)
[MJSONWP]     at GeneratorFunctionPrototype.invoke (/Applications/Appium.app/Contents/Resources/app/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:136:37)
[MJSONWP]     at run (/Applications/Appium.app/Contents/Resources/app/webpack:/~/babel-polyfill/~/core-js/modules/es6.promise.js:75:1)
[MJSONWP]     at /Applications/Appium.app/Contents/Resources/app/webpack:/~/babel-polyfill/~/core-js/modules/es6.promise.js:92:1
[MJSONWP]     at flush (/Applications/Appium.app/Contents/Resources/app/webpack:/~/babel-polyfill/~/core-js/modules/_microtask.js:18:1)
[MJSONWP]     at process._tickCallback (internal/process/next_tick.js:61:11)
[HTTP] <-- GET /wd/hub/session/05bb02df-1826-4178-a698-28e10b580af8 500 94 ms - 394
[HTTP]