Samsung 970 EVO slowing down

When I first installed my 970 EVO, I was getting 3200 Mb/s in Crystaldiskmark. Now it's 1700Mb/s.
Any ideas why that might be?
Thanks.
Windows 10 20H2

Could be any number of things. I had a customer recently whom complained of such issues, turned out they have a recycle bin with over 16,000 files taking up a large portion of drive space. Deleting that data fixed the issue.

More commonly it is a problem with drive optimization. Run the PS command below to trim the drive and see if that helps

Optimize-Volume -DriveLetter YourDriveLetter -ReTrim -Verbose. Replace YourDriveLetter with C: if C is the letter used for this drive.

Thanks guys, I appreciate it.
The drive has only 120Gb of data on a 500Gb drive. And, unfortunately the trim command made no difference. Still stuck on 1700.

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Ok, so IÂ’ve resolved the issue, but....
When I installed my 3090, I have connected one of my SSDs into a SATA socket that disables nvme x4 if used! If I disable that SATA port, my nvme drive goes up to 3600 in the CDM benchmark.
However, I am not able to change the port of the SSD drive in the affected socket as the 3090 is covering the SATA port and I just canÂ’t see how to get the 3090 out!
IÂ’d anyone had a useful suggestion on that, IÂ’d appreciate it.

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OK, I got the GPU card out, changed the SATA port for the affected drive, changed the BIOS setting to x4 on the nvme drive and now all is good again!