Several of our HP printers produce extremely high readings. The transmit discards show gigs in just an hour. And not necessarily when someone prints to them.
For example, I have seen the XMIT reading show 3053% utilization then jump back down.
One of them is in the Top 10 errors & Discards This Hour showing 2,751,846,144 transmit discards.
Do the switch port stats from the device agree with these numbers? If so, it's a device issue. If not I'd recommend a packet capture by mirroring that port and seeing what the traffic actually looks like.