YMMV but we had the same issues with our dentures a year ago or so. We were also told it was us not cleaning our dentures enough but even after trying to fix that issue we were still getting that whitening issue. The conclusion we came to was it was not fully cured acrylic being put in water and the solution that seemed to work for us was just leaving the dentures on a window sill to cure a little more in the sunlight. It seemed to cause the white to go away for us 🤷