The detail that jumped out at me is that even the newer KATO locomotives still stall occasionally, despite the layout running on unitrack with its built-in roadbed. On a modern N scale DC setup like that, I would have expected flawless pickup, so this one is worth digging into.
The layout itself is a solid piece of work. It is N scale DC on KATO unitrack, with track laid on ballast, green ground cover, and paved roadways threading between them. There are multiple track switches and siding sections, which always make an operating session more interesting. On the structure side there is a passenger depot with a green roof, a red commercial storefront, miniature residential houses, and a water tower. The maker has clearly put three years into this, and it shows.
The trouble is that older locomotives flicker their headlights and stall, and the problem got worse after roughly a year away from the layout. The maker tried rubbing the rails with a dry lint free cloth, then went over the tracks and wheels with paper towels and IPA. That helped a little, but anything other than KATO locomotives fitted with capacitors is close to unusable right now.
The open question is what is actually causing the power dropouts and how to fix them. A Brightboy track cleaning block is on the order list, which seems like a sensible next step to me. My own hunch as an outside observer is that cleaning with just a dry cloth was never going to be enough, but the IPA pass should have done more than a little if the rails were the whole story.