POST performance difference between 2017.4.6f1 and 2018.2.6f1.

I test my same script in these two versions. I count the number of post fails, as shown in the following picture.WTF 2018 lost so many POST packages within 10 seconds? The same code works on 17 are smooth and perfect. I once thought because the interface changed. But referred to unity manual, the POST method pages of 17.4 and 18.2 have no difference but some gramma correction. Any comment? Thanks.

My colleague said that Unity 2018.3.2f1 fixed this issue. Let’s see.