I wonder if problems stem from machine washing with powder / fabric conditioner. @Smith and Sharp 's post set me thinking. I have only ever washed mine in clean water in a sink.
Have you ever googled fabric conditioner...? In fact try washing powder too it's terrible stuff, conditioner is full of chemicals and pigs fat, make your towels soft but won't soak up to dry...
I don't let mrs do my towels in it whereas she likes all the smells she can get....