It's probably the TV, this link is about LG but I had problems with Samsung as well.Thanks for that - but since the Toslink sent to a Marantz receiver has no problems I do not think that the problem is with the TV's output.

Latest LG G5 series toslink dropouts
Owning a Hifi store, i tend to change TV sets/equipment now and then. After the last LG, we had two Sony high end TV models and now a LG 65G56LS again. (providing the best picture quality ive seen till now) TV audio playback: over toslink or HDMIarc, depending of video material. Toslink via...
