The order of items in playlists seems to be FIFO (first in, forst out) on mobiles.
It would be nice to be able to apply a custom order, and even shuffle a given list once (e.g. a persistent shuffle). The idea is to shuffle a playlist with a couple of albums once, and finally modify the order to one's liking.
Updated on 2019-09-18
As @Emilia_8 clearly explained, in the mobile app you can rearrange the tracks in a playlist by just clicking the three dot menu in the top-right corner to Edit.
More info is located here:
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