Swapped to my lighter wheels before I went out, I had to adjust the callipers to centre them before I went out, all good.
A few hours of riding about and then get to the top of a steep climb, start firing down it and then try to slow myself coming up to the steep gravely corner, nothing happening!!!
I start really pulling on the leavers, all the brakes are doing are only JUST enough to stop me going faster (its already faster than I wanted to go!), made the corner but still a fair way to the bottom.
So I start pumping the leavers, still no difference.
I finally get to the bottom after about 2mins and only then had the brakes started working as normal!

So, what happened?
Has this happened to any one else?

It almost felt like they were new pads with no bite needing bedded in or there may have been air in the system, but surely if there was, then they wouldn’t be back to normal by the bottom!

Calipers not centred, so one piston is having to press over further than the other?

Foul play? Has your wife recently suggested increased life insurance?

contamination on the rotors burnt off by getting hot going down the hill?

Your inner rad breaking through. You made it down so didn’t need to go slower. Let that be a lesson, brake less.

is “different rotors” nearly the same effect as “new pads” – they bed in as a unit don’t they ?
greasy rotors from handling when you set then up ?

would have suggested contamination as above?