Aha! Now, how did you have your lights set for that?

Looking over my own settings again, here's a complete lighting list:-

Four spots at about waist height inside the blue glow and parented to it, looking out horizontally at 90° angles, set to slightly overlap their light cones and all with "cast shadows" set.

One spot looking up from just below this group of four, same colour and intensity to blend in as best I could try, to illuminate the tuna from below. Set with "cast shadows" off.

One wide-angle spot looking down from ceiling level, directly above the blue glow, coloured neutral grey and just bright enough to let the floor texture show (otherwise it was coming out totally black). Again, "cast shadows" off. This shouldn't have been bright enough to wash out any shadows on the floor.

All props and figures had "cast shadows" on.

I'm stumped. Maybe it's because I have P4 and you have P5 (even with the P4 renderer)...? Have you tried the same scene using the Firefly renderer?