Have you swapped one of the TVs to the other room?
If you move the TV from the bedroom to the living room and the issue exists then it could be the cable or the splitter.
If it doesn't, buy a bigger version of the bedroom TV.
What
Splitter are you using? Are you using RG6 cable? Are the connections tight at the living room TV? (heating up and cooling down?)
1) Check the connections from the splitter to the living room TV. If it is still an issue...
2) Move the bedroom TV to living room to test connection.
More testing.
David