Signa S2 Arc Issue

I've looked through the forum but can't see an answer to this question - I apologise if I've missed it.
I have a Panasonic TH-L42ET60A Television and a Signa S2 Soundbar.
At first ARC worked well - on turning on the TV it would sync and then play only out of the soundbar.
For the last couple of weeks when turning on the TV it plays through both the sounbar and TV with the sound terribly out of sync. If I turn off the soundbar and then turn it back on it syncs and plays only through the soundbar - as it should.
Nothing that I can see has changed.
Any ideas on how I can have it sync properly when the TV comes on?

Answers