Thanks for taking the time to look at this.
I’ve spent quite a bit of time on this today, but just figured it out (or at least I think this is what happened).
There was a library (actually 2 libraries) in my dependencies that had an AOT-compiled jar. This jar contained an older version of clojure.core.cache and clojure.core.memoize.
And, it seems that AOT-compiling messes with library dependencies.
Because of this, cider thought I was using the right version of the library, but in actual fact the compiled version of these libraries from the other library (codax) was used.
Found the jar-explorer tool useful for searching through the jar files in my ~/.m2 directory to uncover this information.