First of all - well done on getting to the 810 stage!
Some CWPC's seem to ignore the "rules" and do their own thing, but for what it's worth, I think you're right to move to 810, especially cos you're about to introduce exercise. You need the extra protein to keep your body from breaking down muscle mass now you haven't as much fat to burn.
Now, the eating thing - really common.

Every dieter in the world recognises this scenario! I suspect some carbs have crept in somewhere and that's what's making it really tough to stick to 810. I think if I were you, I'd do a few days of SS - no more than a week - just to get myself back into ketosis. Then go straight back to 810 - but view it just like SS. See your 810 meal as another shake - get the quantities exactly right, be anal about weighing your veg and protein.

I didn't see any mention of a third shake in your post - have you been having it? Make sure you do - you need to do 810 by the book too.
Don't lose heart, this is definitely just a temporary blip!