I realized now that the HDMI is the problem -_- sorry lol.
This sounds like a Handshake issue. Try turning your TV off, then connecting the HDMI on both, THEN turning it on. Try the device also on another TV and see what happens (different HDMI cables won't solve handshake issues). Preferably, make sure that the TV is 1080p instead of 4K. If you don't have a 1080p see if a friend or relative will let you try it on theirs. If the issue persists, then definitely RMA it. If it doesn't persist, then this may just be a compatibility issue between your TV and the Sager. Usually, 4K TVs have high support, so check and see if there are new firmwares for the TV and install it. Let me know how it goes.
So, it actually turns out that 3 of the 4 HDMI 2 cables I just bought were bad. Oh well, at least it's solved now.