The last few days (Wed-Thu 11/25-26/2015) Samsung apparently released a new version of the firmware for the following 2015 HDTV 1080p models (perhaps other models as well):
J550 J5500 J5900 J5920 J5950 J630 J6300 J6350 J6360 J6400 J6500
Many owners including myself have observed a bug in this new firmware after it uploaded automatically to the TV in the past couple days. When the TV is turned off into standby mode using the remote control, and later when the TV is turned back on with the remote, all the HDMI ports apparently don't wake back up and don't see any signals on any of the HDMI ports.
The only way we have found as a temporary workaround to get the HDMI ports working again for awhile is to do a cold power off (unplug the TV's power cord) for a few seconds and then plug it back in again. Then the HDMI ports all work until the next time the TV is powered off into standby mode with the remote when you have to reset it with the power cord unplug again.
This just started happening in the past couple days after the current firmware version apparently was uploaded to the TV (v1430). I have a Samsung UN40J6300 model for reference and it never had this issue until the last couple days with the new firmware.
Others have reported the exact same problem in the last couple days with their Samsung 2015 TVs in this thread over the past couple days:
I'd like to see how many AVS members with the 2015 Samsung HDTVs have encountered this problem the past few days. Please post what model TV you have and the current firmware version please.
I and others have tried recommended cold resets of the TV (power cord unplugged for over 10minutes, factory reset) but none of those fix the problem. It would seem only a firmware change will fix it. Too bad Samsung doesn't support uploading an older version of the firmware, so they need to release an update version for us ASAP!