I can no longer mediate and completed the main missions upto reaching Skellige. It started at some point at reaching Novigrad at first I thought it was related to the Hatori Swords and Dumplings mission however this does not seem to be the case as I finished that mission without issue.
You can't meditate during combat or confrontation so that may be why you can't meditate. if you aren't in combat or confrontation you most likely just ran into a glitch which can usually be fixed by loading an earlier save, quitting and rejoining the game, or restarting your console. I ran into something similar when I played Skyrim but it ended up fixing itself. If the issue doesn't go away it may be the game or that the issue is stuck in the save file which may require you to start a new game.