Unfortunately that's the facts, and a lot of playlists on Spotify are constantly updated.
As a side factoid I've unfortunately been on here enough to see that some weirdos have previously copied and added entire original Spotify lists that I have to say were the ones I loved the most, so as far as I know you might run into a situation where Spotify just decides to let it go and use a different title with a slightly different name that just confuses everything.
As a suggestion, and not to encourage what I said earlier to take advanatage of Spotify's music, while you see a playlist you like - and before that kind of list you like has some or most of the music disappear - mash-up your ultimate favorites from that list along with jams you pick from radio station samples of songs you choose when you control-click a song and choose "Go To Song Radio" and listen to some of the music, pick out songs that inspire you by control clicking that song on the radio (computer) or simply tapping the song for the menu (smartphone) to make a list that stands out.
Another option to make a playlist of your own that's easy to inspire original songs added to make a playlist of your own is as easy as taking the photo on your computer Spotify software, control clicking that and then choosing "Go To Playlist Radio" or on your smartphone, on the very top right of the playlist album art, click the periods symbol and choose the same option available on the options that pop up there, then do what you did with the song radio and just pick songs you haven't heard from the list that are from the artist or related artists. Spotify...you know how it is.
I've done the same thing on a lot of my playlists. Hope this helps!
If you already have figured out how to activate song radio and playlist radio and know how to add songs to a playlist that already includes playlist songs you took from one you like and created your own playlist, well...you have it down, so try it with R3HAB's new list or one that comes up with another favorite of yours.