I'm happy for you, however, I'm still suffering with the same issue. First time I load the Syria map 40fps, second time 25 and it affects all other missions in any other map after that.
Did all the steps mentioned in the same order...
I have to say that the issue is a lot more prominent in VR, when in pancake mode I can see a drop on fps from about 100fps to 80 to 85 fps, but it is really crippling in VR (likely because is more demanding)