Whisper it quietly but it appears that the latest update + whatever else has happened in the background has fixed my issue. That said I am now careful to ensure I am only sharing on one device (iPhone or iPad), I quit iTunes & restart before embarking on any homesharing listening & I only run iTunes on one machine (the Mac mini) while I am doing it.
I listened to 2 x 2 hour recorded radio programmes, watched 3 episodes of Homeland via my Apple TV and all went well. It strikes me that we early adopters got stung again - remember iTunes Match when it first started (a year ago for me in the UK).
I haven't changed anything on any of my devices - no router fiddling, no switching off ipv6 - just glad I am back to 'normal' for a while
On a slight tangent I see at least one person is excited about the Google Maps iphone app - sadly it is, to me, lame. Clunky interface, no street view & still nowhere ear as good as the old native app.