I understand about the limit of 8 lights per mesh ... this should not be the issue, since I have lots of individual MDLs and any individual MDL does not have more than 3 lights close to it.

What I see is that the lights 9-22 are turned off / not rendered. If I add another light (e.g. in front of or close to one that is being rendered), then another previously lit light gets turned off.

This is exactly what I would expect under A6 with its hard limit of 8 lights.

Very strange ...

Cheers,
Andreas