Getting assigned contracts financed

Hello out there

I have been in real estate for around seven years. Just started assigning contracts. The first short- sale deal was done without any problems when assigning the contract to an investor. The investor lender understanded they were financing and assigned contract. The problem is with the two I currently working on. This investor lender calls it flipping and will not finance the deal. I know this is a pretty long question, however, I wanted it to be clear. I would like to know if anyone out there is having the same problem, and if so how should we deal with it.