Airplay dropping out from iTunes

When I stream from iTunes to my Airplay-connected speakers, it stops playing at random intervals (typically 1-10 minutes). The airplay icon turns orange, and simply clicking play restarts it. This issue has only started in the last few weeks, and I suspect it started with an iTunes update (a guess - but nothing else changed).

When I stream to the same speakers from my iPhone, it does so with no problems.

Any ideas?!

iTunes 12.2.2.25

OSX 10.10.5