Hello,
It sounds like you may have had the mix parameter at 0.
When Tremolo is Pre, the mix control will blend between tremolo and reverb. So if mix is at 0, you will still hear tremolo. With the same mix setting and tremolo Post, you will not hear any tremolo.
Please try troubleshooting this behavior without the HotKnob / expression pedal mapping so you can get the hang of how it works. Let me know if that helps.
https://cdn.eventideaudio.com/manuals/h90/1.9.4/content/algorithms/reverb.html#spring
