WD10EZEX suddenly slow, tests say OK

Hi, I have a 1TB HDD, which became extremly slow 2 weeks ago. File transfer slow, games installed on that drive load slow etc.

I reinstalled Windows (now it runs on a separate drive, SSD, because previously it was on this HDD and the system was extremely slow) and formatted the drive, but it didn’t change. But after a few days it suddenly became good again, everything was running fine. And now 2 days ago it became slow again (programs load slow again, file transfer is slow again, Windows Explorer takes time to show the files etc.).

I checked the drive with chkdsk, I checked it with HD Sentinel, I run qucik test with the Data LifeGuard DIagnostics (PASS), and I even defraged it with Glary Utilities.

I’m out of ideas. I edit videos a lot and it holds me back because the editing program can hardly play the video (when the HDD was fast it had no problems)

Specs:
Windows 7 64 bit
ASRock H97 Anniversary motherboard
Intel i5-4460 3.20 GHz

Data Lifeguard resuls:
Test Option: QUICK TEST
Model Number: WDC WD10EZEX-22BN5A0
Firmware Number: 01.01A01
Capacity: 1000.20 GB
SMART Status: PASS
Test Result: PASS
Test Time: 11:17:42, May 01, 2017

Currently there’s 560 GB of free space

I just run a speed test with CrystalDiskMark, 2 sequence, 1GB

Seq Q32T1 14 and 157 (read and write, MB/s)
4k Q32T1 0.245 and 1.278
Seq 0.629 and 159
4k 0.248 and 1.287

Write seems okayish, and yeah when I transfer files it’s usually the reading that is slow

Weird

I’ll try changing the SATA connection (Cable/Port) and testing that again. If the issue persist, please contact WD support for direct assistance.

I changed the cable with my SSD, but it remained the same