"Я это проверю" was not accepted, is this order wrong?
It's not wrong. According to Rosenthal’s style guide (§ 180.1), both are equally correct. You should report it next time you get this sentence.
Accepted November 2020
Why isn't it я этого проверю
That would mean something like "I will check this one", referring to some (male) living being.
why not ето
There's no "ето" in Russian. "Это" is the correct spelling.