remote stacktrace: UnknownError: An unknown server-side error occurred while processing the command. Original error: Connection was refused to port 50178
11:49:09 at getResponseForW3CError (/Applications/Appium.app/Contents/Resources/app/node_modules/appium/node_modules/appium-base-driver/lib/protocol/errors.js:804:9)
11:49:09 at asyncHandler (/Applications/Appium.app/Contents/Resources/app/node_modules/appium/node_modules/appium-base-driver/lib/protocol/protocol.js:388:37)
11:49:09 at process._tickCallback (internal/process/next_tick.js:68:7)
11:49:09 at sun.reflect.GeneratedConstructorAccessor22.newInstance(Unknown Source)
11:49:09 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
11:49:09 at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
11:49:09 at org.openqa.selenium.remote.W3CHandshakeResponse.lambda$new$0(W3CHandshakeResponse.java:57)
11:49:09 at org.openqa.selenium.remote.W3CHandshakeResponse.lambda$getResponseFunction$2(W3CHandshakeResponse.java:104)
11:49:09 at org.openqa.selenium.remote.ProtocolHandshake.lambda$createSession$0(ProtocolHandshake.java:123)
11:49:09 at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
11:49:09 at java.util.Spliterators$ArraySpliterator.tryAdvance(Spliterators.java:958)
11:49:09 at java.util.stream.ReferencePipeline.forEachWithCancel(ReferencePipeline.java:126)
11:49:09 at java.util.stream.AbstractPipeline.copyIntoWithCancel(AbstractPipeline.java:498)
11:49:09 at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:485)
11:49:09 at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
11:49:09 at java.util.stream.FindOps$FindOp.evaluateSequential(FindOps.java:152)
11:49:09 at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
11:49:09 at java.util.stream.ReferencePipeline.findFirst(ReferencePipeline.java:464)
11:49:09 at org.openqa.selenium.remote.ProtocolHandshake.createSession(ProtocolHandshake.java:126)
11:49:09 ... 53 more
11:49:09
11:49:09 setUp(com.qiyi.cases.bookchoice.function.Test_402748) Time elapsed: 873.163 sec <<< FAILURE!
11:49:09 org.openqa.selenium.WebDriverException: It is impossible to create a new session because 'createSession' which takes HttpClient, InputStream and long was not found or it is not accessible

iOS UI 自动化执行一段时间就会报错，是咋回事呢