Mine has gotten significantly slower on all files and extremely slow on writes.
I'm talking single digit megabytes per second. Also "Active time" in Task Manager is constantly at 100% and everything on the entire computer grinds to a halt. I've only had this drive for one year.
It's about 84% full, but I've never had an SSD slow down this much, even when 90%+ full.
I've deleted enough stuff and retested with 58% full, but it only worked correctly for a short time.
It might be defective, so maybe not related to your issue.
Have you had any luck finding a fix for your problem?