In order for a signal to truly freeze, you also have to turn off modulation. When assigning the hot switch, set either mod depth or mod rate to 0; the Blackhole plugins set Mod Depth to 0 when Freeze is selected.
If your input does not mute, I encourage that as well, to insure the frozen reverb tail does not start overloading. The output is not stably bounded if you freeze and keep playing into the frozen reverb.
