Spotify forces you into this. I have a playlist with a little over 2 thousand songs, and every time I start the playlist it plays the same hundred or so songs because of their shuffle algorithm.
You can use sites like these to randomize your playlist. You can have it randomize the playlist or create a randomized copy if you want to keep the original.
I usually start the playlist, turn on their crappy shuffle to get me to a random position in the randomized playlist, then disable their profitability maximizer shuffle.