Maybe try replacing springs man? I know the valve spring in them can be rated higher or lower or something...but I'm not sure if it would be your issue? Ciaran replaced em before,, they could have been done to a higher rating or something, but I'm not really sure how that works if I'm honest Also, I assume the vacuum hose on the end of the BOV is still connected? Mine popped off before, and it was like it wasn't there at all.
Another small point is that if your changing the nut on top, thats a recirc valve, so just to check piping on that aswel as it should be plumbed back into the turbo. Should deffo hear a difference from one side to the other, I'd say vacuum related if I was to take a stab
Not in any way a guru tho hai. Lol