Unexplained ping delay with "USB to Ethernet" adapter

I am running Linux with old kernel 3.10 on custom board with Huawei HiSilicon ARM Hi3536 chip.The board includes 2 identical USB 2.0 ports. According to HW engineers there is nothingin between of these two ports on PCB board and chip itself, only simple lines.

I am using the USB to Ethernet dongle "USB2-E100" with AX88178 chip.The USB drivers used by that dongle are: asix.ko, usbnet.ko and static usbcore module in kernel.

I connect laptop directly to that "USB to Ethernet" dongle (no routers, switch etc in between).I experience very strange behavior.

When I ping first usb port Round-trip time (RTT) is very stable under 1 ms.

lrwxrwxrwx    1 root     root             0 Feb 16 17:49 1-1 -> ../../../devices/platform/hiusb-ehci.0/usb1/1-1lrwxrwxrwx    1 root     root             0 Feb 16 17:49 1-1:1.0 -> ../../../devices/platform/hiusb-ehci.0/usb1/1-1/1-1:1.0C:\>ping -t 172.20.20.20Pinging 172.20.20.20 with 32 bytes of data:Reply from 172.20.20.20: bytes=32 time<1ms TTL=64Reply from 172.20.20.20: bytes=32 time<1ms TTL=64Reply from 172.20.20.20: bytes=32 time<1ms TTL=64Reply from 172.20.20.20: bytes=32 time<1ms TTL=64Reply from 172.20.20.20: bytes=32 time<1ms TTL=64Reply from 172.20.20.20: bytes=32 time<1ms TTL=64

However if I ping second usb port, every second ping has significantly longer RTT.

lrwxrwxrwx    1 root     root             0 Feb 16 17:42 1-2 -> ../../../devices/platform/hiusb-ehci.0/usb1/1-2lrwxrwxrwx    1 root     root             0 Feb 16 17:42 1-2:1.0 -> ../../../devices/platform/hiusb-ehci.0/usb1/1-2/1-2:1.0C:\>ping -t 172.20.20.20Pinging 172.20.20.20 with 32 bytes of data:Reply from 172.20.20.20: bytes=32 time=873ms TTL=64Reply from 172.20.20.20: bytes=32 time<1ms TTL=64Reply from 172.20.20.20: bytes=32 time=866ms TTL=64Reply from 172.20.20.20: bytes=32 time<1ms TTL=64Reply from 172.20.20.20: bytes=32 time=855ms TTL=64Reply from 172.20.20.20: bytes=32 time<1ms TTL=64Reply from 172.20.20.20: bytes=32 time=841ms TTL=64Reply from 172.20.20.20: bytes=32 time<1ms TTL=64Reply from 172.20.20.20: bytes=32 time=835ms TTL=64Reply from 172.20.20.20: bytes=32 time<1ms TTL=64Reply from 172.20.20.20: bytes=32 time=827ms TTL=64Reply from 172.20.20.20: bytes=32 time<1ms TTL=64Reply from 172.20.20.20: bytes=32 time=812ms TTL=64Reply from 172.20.20.20: bytes=32 time<1ms TTL=64

Can anyone advise what might cause this strange behavior?The same drivers, identical configuration registers, both connected to the same USB hub ...Thanks in advance