Have a Thomson TG585v8 modem and it's going fine, BUT

It seems to be clocking up a sizable amount of what I would say are ATM framing/header errors.
The modem has been up for 28 days and been working without any detectable problems.
Just thought if there's something I can do to better the connection it may be prudent to do so.

The Thomson TG585 is hanging off a CAT5  data line from a VDSL2 splitter.

And the fly-lead is CAT6(didn't have anything else to hand)

SpeedTest returns a constant 12Mbps/856Kbps and stable.

I know I should do my own research, but thought I'd cheat and use someone elses frontal lobe and speed up the process.

Thanks for any advice.