Disable 'use mic qpc timestamps' if they're on. Most likely if you read your logfile, it'll show that the timestamps are too far off, and the segment is being discarded. When it does this, the mic never comes back (even after a mute and unmute). On the other hand, with QPC timestamps off, you'll very likely no longer be able to set up a consistent delay to sync your voice to your webcam input, especially with the variable delay introduced by the VST stack.
One more reason I just went with a hardware compressor solution, and got a really decent mic EQ at the same time; take a look at the Behringer 1204 USB if you have about $120 to invest in your stream. But don't use the custom drivers, they f*** everything up.