Couple more thoughts -
*Higher gravity mashes usually result in lower efficiency.
*Mash not mixed well - dough balls.
*Channeling of sparge water through grain bed.
In my experience, 1.07's is where I start losing some efficiency compared to what I am used to on lower gravity beers. I routinely get 80% efficiency in the 1.04-1.06 range. As soon as I go for 1.07's though, I tend to start falling short of that same efficiency.
I would test the hydrometer though, just in case.
Kegged/Serving: Citra/Mosaic/Galaxy IPA, Blonde Ale, Oatmeal Stout, Amber Ale, American/Czech Pilsner, Farmhouse Saison
Bottled: Bourbon Barrel Maple Coffee RIS
Primary: Czech Dark Lager, Oatmeal Stout, American Amber, Blonde, Citra/Mosiaic/Galaxy IPA
Future Brews: Scottish 70, Dark Mild, American Pils, Bo Pils, APA....... More...... More....... Beer.......