upperdir is in-use by another mount

I just built a new image and enabled overlayroot. Super smooth; this is very cool!

I see the following warnings in the journal after boot, however:

Jul 05 19:46:21 pizero kernel: overlayfs: upperdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.
Jul 05 19:46:21 pizero kernel: overlayfs: workdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.

I don't know enough about overlayfs to say if this is a concern, but it did raise an eyebrow.

I have no idea what could be causing this... Did you find any additional information?

I have not. It’s been working fine for me, however.

What does a simple 'mount' command give you? You should see all existing mounts there.