1st post, please be kind

I have an application where we are using a TR80x10-7e trapezoidal thread to tighten a nut pulling two parts together. For simplicity you can consider it to be a simple nut and bolt but with the TR thread.
Screw material is 17-4ph stainless steel and nut is CA104 aluminium bronze.

Once tightened we need to release the screw and what we're seeing is that the torque needed to release the assembly is higher than that applied to tighten it.
I've ran simple tests and seen consistent results that removing the nut once tightened is requiring ~20% more torque. I was under the understanding for all of my engineering life that undoing a screw should always require less torque than applied to tighten it? In my application we have the same torque available for tightening and releasing so the assembly is not releasing and machine is breaking down.

It's my first real use of Trapezoidal threads and I'm doubting everything. Could material choice be an issue? Are TR threads different from normal?

Any advice would be greatly received.

Thank you