I manage to workaround the issue for now by putting TB in offline mode shortly after it startup. And then put it back in online mode. Then both email/calendar seems usable after a short while without the Not Responding issue occurring. But really not an ideal situation... this issue also seem to cause some unexpected side effect Bug 1642580...
Bug 1642292 Comment 4 Edit History
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I managed to workaround the issue for now by putting TB in offline mode shortly after it startup. And then put it back in online mode. Then both email/calendar seems usable after a short while without the Not Responding issue occurring. But really not an ideal situation... this issue also seem to cause some unexpected side effect Bug 1642580...