Intermittent Connection Problem Between Active/Stanby LTM 1600 and a pair of Cisco 2960

More to add, actually the LTM is running in route mode which all server points to the LTM as the default gateway. In addition, the Internal LAN is solely a subnet dedicated for F5 load balancing and thus only one vlan 4093 with IP (192.168.*) exist. While the External WAN consist of a lot of different subnet but the native VLAN is 10 with IP (10.1.*). I have tried using access mode for Port-channel 3 for both LAN-2960-A and LAN-2960-B but still encounter similar packet drop. Just wonder which part of the configuration could go wrong causing such intermittent connection problem.