It seems that one of the organisation settings at the top of your playlist may have been selected. Check the top of your playlist and see of any of the column headings looks like the Artist one below.
If it does, click on it a couple of times, and it should go back to normal.
I take you are running an android spotify apo. If you load up a playlist and then swipe down from just under the big shuffle button, just an FYI here you do need to be a permium subscriber in order to play in the order that you wish to. But if you are permium keep swiping down from underneath the big shuffle button until you see then a filter screen. On the far right is a kind of odd looking three line icon, tap it, you should get filter options. If this does not work you must be stuck in shuffle mode, and either need to be a permium user to turn it off or need to go back to the playlist view and tap on the current playing song at the botton to show the Now Playing Window, to turn shuffle mode off here look to the lower left for a double crossed arrow turned green, keep tapping until it turns back to grey. Does this help any?
You can only sort stuff if none of the columns selected for ordering AND you have Queue play mode selected!
Spofity, you need to fire all you dumb UI/UX experts it is just nonesense.