I saw this today in FCP warnings. Searching around I found it looks to be hardware/driver/firmware issue. The only hardware change is that I recently moved the OS thumb drive from usb3 to usb2 after advice from:

https://lime-technology.com/forums/topic/70174-os-flash-drive-w12m-writes/?tab=comments#comment-642941

 

One thing though, I couldn't get the bios boot preferences to recognize the usb2 drive but was able to see it in a boot override screen. Bad usb2 ports? 

unraid-diagnostics-20180417-1550.zip

Try upgrading to v6.5, different kernel can make a difference, but IRQ 16 seems to only be used by USB, so if you don't notice any issues you can ignore.

I'll give it a try. To be clear, you mean prerelease v6.5.1.-rc6.

or v6.5 since your still on v6.4

You have a choice of 6.5.0 or 6.5.1-rc6, depending on whether you want to stay on the stable branch or not. Personally, I'd go with the newer 6.5.1-rc6.

Wow, didn't know 6.5.0 was out! I had to got to Tools>Update>CheckForUpdate to see that. I could swear a new update alert used to show up on the gui banner.