I just bought WDS120G2G0A, have the same problem
crystaldiskmark 1cylce, seq read and write results:
100MiB = R 473 ; W 293
500MiB = R 483 ; W 123
1GiB = R 496 ; W 90
2GiB = R 487 ; W 92
so this is normal? when we test with large file, SLC buffer can’t handle large file ?
Use Windows 10 x64 1709
------- update 1---------
I back to the store I bought yesterday, they replace with new one, still WDS120G2G0A
Then I benchmark it, seq R 500MB, W 230MB
but after few usage and data written (install windows in it), seq W drop again to 70-90MB/s
I tried format the ssd, and boot use other windows partition, then benchmark again the ssd, seq W still 70-90
Then I try the ssd on my win 7 notebook with 2.5" enclosure USB 3.0, write speed still 70-90MB/s
2 same ssd with same results, low Write speed ???