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I recommend contacting Customer Support and asking them to restore your collaborative playlist to an earlier state; they’ll take a look and do their best to help.
Also, there is currently a Live Idea in the Idea Exchange of the Spotify Community for limiting editing access in collaborative playlists. If this is something that you’re interested in, I would recommend adding your +VOTE to this idea. The more votes an idea gets, the likelier it is that Spotify will implement it; and you can read more about how feedback on ideas reaches Spotify here.
Let me know if you have any other questions, and have a good day!
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