Reorder button of collection not appearing

Something weird happened to me: I can reorder the entries in one collection, but I can't do the same in another collection. The reorder button is not showing up (check screenshots below)Is this something you can change in settings somewhere? Can't seem to figure it out.

With button:

Without button:

Anyone has an idea? Thanks in advance!

Answered by Maarten Lauwaert!
>>>>>>> Answered <<<<<<<
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