1 ) Overfeeding pellets
Feeding too many pellets can cause rabbits to become overweight and can cause problems with their digestion. Increase this a little through winter or when rabbits need to gain weight.
2 ) Feeding muesli type dried food
Rabbits will pick out the bits they like and leave other bits which mean they are not getting all the right nutrients and that will lead to lots of health problems. A pellet only dried food that consists of at least 18% fiber is a much healthier option.