What can cause narrow disc brake gap in TRP Spyre-C? I have mechanical disc brakes (TRP Spyre-C), second year. Last year I removed and mounted wheels without problems. This year I am all surprised because I cannot adjust the rear brake.

Front -- no problem, plenty of space between brake pads. I can insert 2.5 hex key between pads and even tilt the key a little. Next I can screw in pads-screws, and then fine-tune it with the barrel.

Rear -- I cannot even insert 2.5 hex key between pads (in their neutral position). So basically I can barely put the wheel on, but I cannot adjust brakes at all.

Did I damaged something? Is there is some element extra to adjust?

I already checked and rechecked:


cable tension -- cable is completely loose
barrel adjuster -- all way in (meaning it cannot be shorter)
pads-screws on both sides -- (un)screwed outwards 
pads wear -- I just put an identical pair on front and rear


I also removed pads, cleaned the interior (I was thinking about some sand grain), no change.

Granted, last year rotors where 1.9mm thick, current ones 2.0mm, so maybe this explains why I was able to put the rear wheel (but I am sceptical), but the problem remains -- why such a difference between gaps? Could it be my rear brake is faulty (by manufacturer) and I simply didn't notice? Or there is some magical screw (to fix it, or disassemble it)? Is there a way to remove the brake lever (the one at the brake, not at handlebar)? 

Any help in solving this mystery is welcome!

Background details:

I upgraded in the rotor diameter as well, front from 160 to 203, and rear from 160 to 180 with appropriate adapters, just as sanity check I unscrewed brakes from adapters and it didn't change a thing.

Last year -- Sudden gap between disc brake and pads? -- I got mud (?) in front brake which had curious effect -- it didn't damage anything, at least I didn't notice, it didn't peel off the pads, yet it widened the gap of the front brake. So from current perspective it looks like it was a fix-therapy and I wonder how I can perform such fix-therapy for rear brake on demand.
That's an uncommon problem for mechanical disc calipers and I have a guess what's going on.

Spyres and Spykes are generally good brakes but they have the quirk that the pad adjusters can get a little stuck. When this happens, the adjuster will feel seized, but if you're only trying to turn it out, that could be mistaken for it being retracted all the way. Try turning it both ways to confirm it's moving freely.

If it is stuck, what's always worked for me is take a higher-leverage 3mm wrench in very good condition (to minimize the risk of rounding the wrench flats) and just pop it free. It can take more force than you'd normally want or expect to be putting on a 3mm allen, and when it frees it makes a scary 'pop,' but then works normally again. 

If both pad adjusters are known to be moving freely and all the way retracted and the cable isn't even attached and the arm is known to be all the way in its starting position, that kind of only leaves some kind of internal problem with the brake, and I don't know what that would be.