The same branch is shared by a bathroom (toilet, shower, sink) and those bathroom drains have never had a clog. Although they always periodically stunk despite full traps so I suspect a leak was always there. But since it’s only occasional I wonder if it’s a leak at the top of a pipe, not spillage. Well, otoh there might be spillage going on in the bathroom because there are drain flies, which might be feeding on spillage from somewhere. It just seems bizarre that the odor only manifests occasionally.
The big branches meet at a main Y connector. That Y connector is new. The basement had a serious leak under the concrete a couple years ago. The basement floor was dug up and new pipe was installed. I doubt there would be any issues with this new pipework. I think the only segment that’s quite dicey is from the kitchen sink to wherever it joins the bathroom.
(edit) are you perhaps thinking that the clog has moved along and will clog again downstream? I doubt that, because the diameter of the kitchen drain is 40mm and it eventually joins a branch that’s like 90mm in diameter. If this thing were to snowball for some reason, it could probably be reached from the cleanout at the main Y fitting, no?