AMP stopped playing the tv and it won't sync with the tv no more

hi,
My amp sync with the tv is lost since last week and they won’t sync anymore. 

since I bought the amp 6 months ago, it had no problem synching with the tv via hdmi arc.
I just hooked hdmi cable from the tv arc exit to the hdmi port on the amp and bam, it worked.

not anymore :(

since it stopped playing tv audio last week, I tried a few simple actions to fix it and bring the amp to play the tv sound back again,

a. I tried to use a different hdmi cable

b. I reset the amp and hooked it back to my system.
c. I  connected an apple tv  to the arc/hdmi-2 input on my tv , just to make sure that the hdmi connector on the tv is ok and operational , and it did work fine  (the arc port on the tv works both as an arc channel and as an output hdmi channel)

help needed :)