I would view those pancakes the same as most other treats for chickens: safe to give small amounts regularly, and no real danger if they pig out once or twice, but do not give large amounts as a regular thing.
There is nothing specifically dangerous in the pancakes, they just do not contain all the nutrients a chicken needs.
The common "complete" chicken foods are made so a chicken can eat them and nothing else. For anything else, eating large amounts of one food will usually mean the chicken eats less of other food, so it misses out on some of the nutrients it needs. Or the chicken eats enough to get all the right nutrients, but eats too much total food and gets fat.