Odore persistente dopo tinteggiatura senza muffa

Hello everyone,
Context: 25 year old house with two layers of paint on plaster repainted 6 months ago half by a craftsman and half by myself.

The portion that I repainted has zero problems while a part of that treated by the craftsman (a room and a closet) develops an annoying smell similar to that of onion that passes only temporarily by ventilating the premises.

I treated the walls with an acrylic insulator, the craftsman no, the paints are still different.

I specify that:

- no room has or has ever had mold problems
- the 2 rooms that develop odors are not affected by walls with vents, drains and the like and in any case did not develop any odors before repainting;
- in theory the craftsman used the same washable paint for all the rooms he treated, in practice this is not verifiable;
- the continuous stirring of 10/12 hours a day for months does not resolve, after 1-2 hours after closing the windows the smell returns;
- the worst smell further sleeping in the affected room, I think for the humidity of the breath;
- the use of deodorants has a temporary effect, removing the smell returns with a slightly modified stamp;
- the rest of the house does not present any problems of this type;
- the paint used by the craftsman was in his opinion new and in any case the advanced portion did not stink.

I come to the questions: what can be the causes and above all ... how do I get out? :-(
I asked a couple of professionals who suggested that we scrape off all the layers of paint, old and new, and do it all over again.
It seems to me a cyclopean work, the old painting was well anchored to the walls, like the new one on the other hand, the amount of work to remove it seems to me considerable.

Can other ways be tried, such as washing and / or a specific layer of insulation and a new coat of paint?
At present I am avoiding using the room but soon I will be forced to do so, as it is I think it is harmful to health as well as annoying.

Thank you