Disk Performance Problem

Hello,

I bought SSD Ultra 960 In 2020 and mounted it into imac. First 2-3 months it was working fine but since two days performance is very bad. When I check the disk speed with a disk tools it says around 5MB per second for write. Current firmware version is : Z33130RL.

Is there any updated firmware for this disk? Or what should I do to resolve this problem? Is there someone that meet with same problem before?