My bet is this is our old nemesis called the HDMI HANDSHAKE or BLINK.
Frankly HDMI has earned no love from me but try the usual before you call it in. Power off, remove all cables then remove the power cord for 10 or so minutes. Attach the power cord and the one HDMI you want to test with and try again.
My Tv just turns off then back on every hour. It turns off for about 5-10 secs.