IIRC, it was mainly banned because "there is consensus that The Grayzone publishes false or fabricated information" (as the summary states). I believe this was one of the examples: https://www.thedailybeast.com/in-nicaragua-torture-is-used-t... (Grayzone presenting the forced confession of an anti-regime activist as legitimate). Here's another about Max Blumenthal himself fabricating a quote: https://www.theatlantic.com/international/archive/2011/12/di.... There were questions about its editorial oversight, but those were secondary. Basically it's one of those sites, like RT, that has a political position and has little problem with pushing disinformation to support it.