USB dropout.

[agent_kith]

Received your diagnostics file.
 Everything seems to run good, then about 67 minutes in, the USB port is resetted. I'm not entirely sure what/why it's doing that. There is an option to reset the USB ports in the System menu. Don't think you pressed that button by any chance, did you?
 [   21.793171] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
[   44.002167] cgroup: new mount options do not match the existing superblock, will be ignored
[ 4021.250023] usb 2-1: reset high-speed USB device number 2 using ehci-pci
If you didn't reset the USB port yourself. This means Linux has done that for you. And it only does this if it detects a problem on the USB - transfer errors, low power, etc.Is this a USB port on the motherboard, or a external card (e.g. SoTM, JCat, etc)? If possible can you try another port and see how it goes?
The idea now is to isolate where the cause is, try the following:

1. Use a different version of MPD (v19, 18 or the old v17)
   
2. Try a combination of different USB cable on different USB ports and see if it still behaves the same way.