The lens correction for the Olympus micro 4/3 lenses should be applied by Lightroom when you are working with raw files.
If you are working with jpeg files there is no need for Lightroom to perform a correction since it has already been applied by the camera firmware. If you need additional correction you can apply manually in Lightroom.
Quote "Why are they "hidden" corrections (if they are there at all)?" The lens design for the micro 4/3 are such that they require specific lens correction, this allows the manufacturer to reduce size, weight and cost of the lens. The Micro Four thirds camera apply the correction when producing jpeg files and the necessary correction is stored in the raw file header. Lightroom / ACR and some of the other major raw conversion software apply the correction for the raw files at import. There is no option to turn the correction off.
For your camera which has built-in profiles, the working of the message is different depending on whether lens profile corrections are enabled or not.
Without a checkmark in Enable Profile Corrections, you see a message that your camera has built-in profiles that are applied automatically. This is what you remember seeing, before.
With a checkmark in Enable Profile Corrections, you see a message that it can't find a profile, which is true since you're asking LR to find an external, optional profile for your lens and there isn't one. That doesn't mean that the built-in corrections aren't being applied, anymore, they are, it just means there is only one place to have a message and LR can't both say that built-in corrections are being applied and that it can't find a non-built-in profile.
That makes sense; as you describe, with nothing checked in the "Lens Corrections" (Profiles) tab there IS a message saying a built in correction has been applied, and then if you click the box it says no correction can be found.
Somehow I hadn't noticed the difference that checking that box made....
All is right with the world now!