4K output messes up lighting

[ViggoPaulman]

I have a bookcase filled with individual 3D books.
They’ve all been imported as Enscape proxies to not choke SketchUp.

Could someone explain, why a 4K render produces this buggy lighting, and the 2K version renders everything ok?

The issue seems to be connected to the books, because removing them and trying a 4K output again produces this (correct) result:

So this is a double-edged sword; from one side I presume it’s caused by the books. But from the other side it’ also connected to the output resolution.

All the books are low-poly 3D assets, imported as Enscape proxies. The bookcase itself is also a proxy. Here for visual reference:

This should not happen on a 24GB RTX3090 with 64GB RAM!

What can be done to resolve this? We cannot just render in 2K because we need the superior resolution.

This is on Enscape 3.5.6, Windows 11.

[ViggoPaulman]

I would like to report, that even the 2K render is wrong. It merely reduces the buggy lighting, but it’s still there.

The viewport preview shows a visually different image, with deeper shadows.

Pay attention to the shade near the radiators.