Unreal Engine is installed on my SSD samsung pro 512 Gb (not partitioned), so it’s not a matter of drive, or partition.
Looks like it’s not a memory usage issue too… well ^^ I noticed that box reflection capture has an important risk of making the building process crash, I also noticed that by rebooting the engine, and building lights first, it has more chance to work.
So I managed to make it work on production quality on a very modest indoor scene I build myself from starter content assets, that’s how it looks :
I do not have a box reflection capture, just a lightmass, and I didn’t tweaked the lightmass, that may explain some visible artifacts around the white light lamp (static spot light). Well, I don’t want to go off topic too much but that’s how production quality looks on a housemade little scene with minimum tweaking 