Room smells like marijuana or hashish

That already happens upon suspicion report

A mere assumption from the OP is not sufficient here.
The dog would have to alert = suspicion.

Do you think he stashed something there?

There are countless hiding places 8-).

The phenomenon that human sweat can smell like [grass] is also known.

What kind of building did you live in before? Is there a ventilation system? How often is ventilation done?

interesting post *push*

I have a 3D printer. When it runs, the grease gets warm and it also smells like a large plantation

Hi,

my 3D printers print with PLA (at least I only use that, no ABS or TPE)
That also smells strange, but clearly different from "weed". Somehow sweetish?!?
(it is also made from polylactic acids)

I know the smell of weed very well. My wife's son spent some time in
his room (in our house) with his friends consuming "small" amounts.

I'm not going to read everything through now but do you have vinyl flooring in the children's room? The plasticizers smell similar, the different times can for example come from the sunlight exposure.