I can reproduce this reliably:

While there your user has a "playing now" with a recording that is properly identified and linked to a release with CAA cover, open the user's listen page.

No cover art is displayed, instead it shows the "Add cover art" placeholder.

Now stay on this page and change the "playing now". You can switch to the next track, or then back again to the original track. Cover art is shown as expected.

While the track is still playing reload the page, the cover art that was just shown is gone again.

Once the same track gets submitted as an actual listen the cover art is shown in the listen list all the time.