Happens as well for the Nari Ultimate. For me it appears to flash the red led for a moment, but then quickly turns it back off, checking synapse shows that it did mute (most of the time, but not always). Worked fine with synapse 3, only happening with Synapse 4.

Also, can my mic please stop resetting back to 50% randomly? My discord buddies complain 2-3 times over a two hour session about my mic getting quite, and sure enough checking synapse shows that its back to 50%.