Ive had this happen several times over 30 years... this is why i went to Fresh Kill. I worry about snakes under 500 grams. Im really not interested in frozen for several reasons myself. If you like the Frozen idea then maybe try ordering some (stay away from Petsmart as they are 3 times the price online at RodentPro) and trying it..
As far as the other situation it happens but isn't common. I wouldn't worry. There are times they just don't get a good grip either.