One t-shirt gruffles, the other not
Muffling laundry has been written here a lot, but a problem is still waiting for the right tip:
Some in my T-shirt collection do not muffle others (fresh from the cupboard). Same machine, washing powder, material, color.
Leave several T-shirts in a vinegar solution (one cup of essence per liter of water) or a solution of citric acid (common coffee machine decalcifier) for a few minutes.
Some of my T-shirts were * once * too long wet. (Sweaty in the laundry basket, after washing too long in the machine, once wet in the closet).
On the occasion, microbes form, surviving the 40-degree wash or even weeks of drought in the closet, sun and fresh air. As soon as you put your shirt on, heat and moisture (easy sweating is enough), these microbes live up and spread their "scent".
The acid in the vinegar or in the decalcifier reliably kills the microbes.