Network instability and packet lost (only 2 pings)

Hello,

I have a problem with my network that is driving me crazy. This is a Fortinet network (Fortigate, Fortiswitches, FortiAP, Fortimanager, etc)... There some users that need to use an application that crash when it lost connection or if there are delays in the network... The only thing I can find is that those users lost 2 pings every time they get disconnected from the server. I don't have loops, there's no high CPU or memory, I haven't packet lost counters... I had check almost everything I can imagine... Does anyone had had this problem before? or something similar?

Thanks in advance.