I had been walking this shadow Feebas when Mega Master League started and I switched buddies to my Gyrados for the cp boost.
Switched back to Feebas today via buddy history which brought me to the buddy tab. Scrolled to check how much distance I had and to my surprise the Evolve button worked. I've now got a Milotic in 1/4 the distance.
My suspicion is Gyrados's distance somehow carried over since I hadn't closed out of the buddy tab, except it didn't work swapping Gyrados on a second Feebas – I likely had walked Gyrados over 20km without swapping on the first one.
by dan2872