One of my posts was apparently edited, but looking at the history, I see no visible changes. What happened here? (This question is motivated mainly by curiosity, but there must be some sort of bug in play.)
The edit description says "edited tags". I'd assume that the editor added/removed a tag which no longer exists and therefore doesn't show up in the edit history.
A little sleuthing confirmed my guess. Using the Wayback Machine, we can see that in its original post-edit state, your question had the tags tolkien and middle-earth, both of which were merged into the new franchise tag tolkiens-legendarium during the Big Edit Event before being separated out again. Presumably you'd originally posted it with just one of these tags and the editor added the other one. But the tag merge mapped both tags to tolkiens-legendarium everywhere in the database, including in revision histories, so this became a null change.