Engine hang while a flow have multiple reply activities

[lixingwang]

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[*] bug report => search github for a similar issue or PR before submitting
[] enhancement request
[] feature request
[] support request
[] general question

Current behavior (how does the issue manifest):
Configure a flow with branches and multiple replies activity(reply to Trigger)
Expected behavior:
at least no hang, need a way to avoid or handle multiple reply
Minimal steps to reproduce the problem (not required if feature enhancement):

What is the motivation / use case for changing the behavior?

Please tell us about your environment (Operating system, docker version, browser & verison if webui, etc):

Flogo version (CLI & contrib/lib. If unknown, leave empty or state unknown): 0.X.X

Additional information you deem important (e.g. issue happens only occasionally):

[lixingwang]

flogo.json.zip

[lixingwang]

Reproduce steps:

Run command 5 times. the 6 time will be blocked. curl http://localhost:8888/path?id=122
Because all 5 works been blocked