I would try getting a cable cord long enough to reach the bedroom then put the cord in line with the living room and make sure there is no difference with the present setup, then take the length of cord and feed it to the bedroom and see if things get any different.
It is a process to check each piece of the connection, always start with the easiest. I eventually found that the center wire of one of the cable connectors was about 1/16th of an inch too short to make proper contact in the female end of the connector it was screwed into.