Lightmap baking problems - Same model -> some instances work fine, some are completely black?

Hello everybody!

I’m pretty new to Unreal Engine, but I seem to find my way around pretty good so far.
There’s one problem though I can’t find an answer to.

I have an a model in my level that’s lit with a static light.
There are a couple of instances and some of them just work fine, some of them are completely black.

I googled and found a couple of posts that were fixed by fixing the lighmap resolution / UV maps etc.
This didn’t work for me though - and still, wouldn’t be every object black in that case and not just some instances?

I attached 2 images - both objects are the same model, I just changed the scale individually.
Each one is lit by a static light for demo purposes and the lightmaps are baked.

Would be great to get some tips - thanks in advance!

PS: the candles and candle holder are two seperate objects - candles work fine.