downloaded pdf is blank

i have 2 virtual servers each one with asm policy and share same pool member. the first virtual server has a blocking security policy ,wan acceleration profile and http profile the second virtual server has a transparent security policy and wan acceleration profile and http profile

when i download pdf document from virtual server 1 >>> it downloads it but it's blank when i download pdf document from virtual server 2 >>> it downloads it correctly

when i look to asm event logs there is no illegal requests and there is no violations as well. can anyone help me about the reason of this issue???