This is happening for me as well - just tried it. Adding the second instance as VST crashes the host. It does not halt when running in the debugger, though, just crashes the host. I tried with Reaper and Cubase 7 and both crash when you add the second instance. Also tried Reaper 32 and Reaper 64 with same result.
Some notes:
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The VST3 version does not crash the host, only the VST-wrapped version.
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The vst wrapper function create( ) does succeed (both times) and returns an AudioEffect*
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The GUI does show up for the second instance, but the host locks / freezes right after it is shown
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The crash only happens for Windows clients; Reaper on MacOS did not have issues
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Will