Thanks for the post. I have checked the repos and no third party - it seems like something went wrong with the install like netblues above. I do have squidguard installed.
In the end, I basically did what was described above (with some detail in case it helps someone else):
Connected WAN to a wifi hotspot (which was a little more painful than I hoped). This was helpful: https://www.youtube.com/watch?v=qRyXAFD94lI
Used pkg upgrade -y mpd5 in Diagnostics/Command Prompt to force the upgrade of the package
Confirmed upgraded with pkg info | grep mpd5
Changed WAN back to PPPoE connection
Hopefully this is a limited issue. Was a bit painful but learnt some stuff along the way so not all bad.