I just experienced this exact issue.
Mechanical clicking, under heavy brake load. Nothing under light braking.
Turned out to be the spring clips, that the H Bobbin sits in, in the front rotor hat:
The wing thingy broke free, from the rest of the spring clips and worked itself proud of the hat cutout. When the brakes were applied aggressively, the pads would interfere, with the clip.
I have new clips on order, and will be replacing all 20.
Not sure if this is your issue, but the way you describe it, it sounds similar to my failure.
No pix, yet. I'll post a thread, when I get the parts and do the work.
Bob