4K Write IOPS performance lost

[Matas]

Hi guys,
I am using Iometer for testing SSDs but recently faced mystical situation when having same options in Iometer Kingspec Challenger 120 GB SSD can't go through 40000 IOPS in 4K 100 % write test (repeating pattern) any more. It was doing ~65 000 IOPS previously. Tried secure erasing but nothing helps
May I get some opinions?

 

[staticlag]

Google: Garbage Collection and TRIM in SSD

I'm having trouble posting the link

 

[Matas]

As I said secure erase was performed so SSD is in fresh state but doesn't help. There is no point about GC and TRIM here I think.