Terminal 22 touches the #8 nut that sits above it. The bolt that passes through that touches the transformer cover, the transformer cover is grounded through the screw by the IEC inlet.
The insulator is there to control how the transformer is safety grounded.
Great, I see your points now.
I think the heavy painting on my transformer cap breaks the ground path. I painted both sides of the transformer cap with multiple layers of paint. So it much be the paint on the cap that breaks the ground path from T22 to the #8 ground solder tab connected to the chassis.
However, I think the grounding of the transformer itself in my case is still OK, because on the other side of the transformer the T16 terminal connects the transformer to the ground, and this ground path is not affected by the painting. It's just T22 and the painted transformer cap are not grounded - but I think it doesn't matter.