xctrunner quited退出问题 AttributeError: 'NoneType' object has no attribute 'conversation_index'

[D 210324 18:52:55 _device:942] logProcess: t = 24.55s Requesting snapshot of accessibility hierarchy for app with pid 3966
Exception in thread Thread-2:
Traceback (most recent call last):
File "d:\appstore\python37\lib\threading.py", line 926, in _bootstrap_inner
self.run()
File "d:\appstore\python37\lib\threading.py", line 870, in run
self._target(*self._args, **self._kwargs)
File "d:\appstore\python37\lib\site-packages\tidevice_instruments.py", line 558, in _drain
self._drain_single_message()
File "d:\appstore\python37\lib\site-packages\tidevice_instruments.py", line 578, in _drain_single_message
mheader, payload = self.recv_dtx_message()
File "d:\appstore\python37\lib\site-packages\tidevice_instruments.py", line 499, in recv_dtx_message
assert mheader.conversation_index in [0, 1, 2]
AttributeError: 'NoneType' object has no attribute 'conversation_index'
[I 210324 18:52:55 _device:1114]
xctrunner quited

什么原因造成的运行中途退出，随机出现此问题

Start with tidevice_instruments.py, especially _drain, _drain_single_message, and recv_dtx_message around the reported assertion, then trace how _device reports that xctrunner quit. Reproduce the intermittent failure and determine why no message header is returned; done means the cause is documented and the run no longer exits unexpectedly.

Written by the indexing model from the issue text.