The first review for the slippers is 1 year after I purchased them. The tongue completely detached from one slipper. The usage I put them through is demanding for the product since I wear them constantly. I wore them every summer, all summer long, wherever I could. I even went into the sea with them on rocky surfaces and they were underwater for half an hour several times. (The insole can be easily washed with soap and water)
The tongue, where it is attached to the sole, is made of fabric and glue is used on the side where it stands. It seems that if the slipper gets wet many times, the glue weakens and that's why this happens in the photo. I don't think it happens because of the sun or heat.
If you want them to last, try to avoid getting them wet as much as possible.
I won't buy them again, I will look for something else.