I wonder if the shining effect of Mosaic Slimes are still bugged.
Putting a Mosaic Slime in a Solar Shielded Corral then destroying it would keep its shining effect turned off. Dragging a Mosaic Largo out from a dark cave (such as the Grotto) by having it on the vacpack nozzle would also keep it turned off. However if it wandered out on its own, it would behave as normal. A Largo with its shining effect off when it went in would then have it turned back on when coming out.
Edit:Can you tell which one was in a Solar Shielded corral?
Now for the Grotto:
The glistening effect is less obvious but it's there.
Dragging it out of a dark cave via the Vacpack nozzle. Notice the last of glistens.
Dragging it out by the vac stream from the entrance. Interesting enough the glistens were turned off where the entrance is usually illuminated but turned back on when coaxed further out.