as we see in this image, i'm using a sub kyu-b with freeze shock second slot and ice beam fourth slot. where's the confusion? just tick z-power and click slot 2 to use your z-move!
uhm excuse me what the fuck? i click z-power and then click slot 2, as i'm regularly used to. and...
now i'm sure for anyone that has used any pokemon with two potential z-moves (beam + shock kyurem-b, hurricane + defog tornadus-t, edge + rocks or fly + defog landorus-t) you would be accustomed to THIS menu instead
pretty nice design, keeps the moves in the same slot. has been the same way since the dawn of time. but apparently someone wanted this to be changed and there wasnt much of an announcement, so here it is for anyone wondering.
the solution is to make sure that your intended z-move (freeze shock, hurricane, stone edge) is in the first slot or have it in the second slot with your unintended z-move (ice beam, defog, stealth rock) in the first slot.