This answer generally focuses on how to reduce wear on cycling clothing during washing. I am not convinced that spandex or other synthetic fibers would be damaged by chain lubricant or sunscreen (as in I don't think those substances cause the chemical bonds to deteriorate, whereas chlorine will attack some synthetic fibers and weaken them over time; ...
I have some shorts that have worn in one spot, and I have worn them less then 10 times.
(someone?) said that it comes from friction, but at the front of my leg?
So now the shop say it's from friction in the washing machine. That could be the cause of your clothing deterioration.