I broke a fast with real pizza a while back with 140 carbs worth of an all meat variety of pizza. My glucose shot up to 140 and my ketones fell from 6.3 to 2.1 in the couple hours that followed. The next morning they were up in the 3ās and the days that followed they stayed in the 4-5 range while intermitant fasting. I never fell out of ketosis and in fact by non-fasting standards stayed in deep. I think due to the fasting my glycogen stores were depleted and the 700 or so calories of carbs went primarily to replinishing them. The insulin response to the carbs was definitely seen with the ketone drop, but whatever carbs were not turned into glycogen I believe were quickly burned off and ketone production was taking place in a a matter of hours after my meal, as I saw the evidence with my blood test when I woke in the morning. I also only say about a half of a pound increase in weight, so not much if any real water retention took place.
I was 14 months Keto when I did this little n=1 expirement. It was interesting but when all was said and done I would have enjoyed a ribeye more then the pizza that was at one time my favorite food to eat. If I had not been in a fasted state when I ate the pizza I believe I would have been kicked out after the meal but more than likely back in the next morning. My ketones are usually in the mid to upper 2ās when I am eating my normal Keto routine. Maybe I will try it out sometime just for kicks.
Just thought I would share a similar experience I had, not sure if it is any help an any way, but what you experienced is not unique.
Remember everyoneās tolerance for carbs is a bit different depending on metabolism. What may kick some out and set them back for days may not do the same to others. Some have to keep carbs around the magic 20g a day to stay in nutritional ketosis while others could have three times that amount. Just another reason why it is so important for everyone to figure out how their unique bodies work.