Permalinks have extra space character at end, why?

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I just noticed that while my permalinks looked correct when I click on them or in the browser URL address bar, they actually had a extra %20 space character at the end.
I found this when I did a “Copy Link” on the Permalink: link at the Edit Post page.
Ex: https://www.example.com/some/path/%20

I wrote some PHP code, and sure enough, calling get_permalink(id) returns the same extra character, on all of the ids I checked.

Any hints on how to fix this, or what I should investigate next?