Technically while it doesn't suit his game perfectly there is no reason for such a poor record at Roland Garos. Hell, even John Isner has a better FO record...
Those 1st round losses here and in Rome through the years makes me think he just HATES playing on red clay; doesn't mean when Medvedev is "on" he can't do well occasionally but mentally I just think he checks out. The dust, the skidding and sliding on the surface, the marks on the court to determine calls, etc , for what ever reasons I just think Medvedev isn't comfortable and can't wait to get off the court. He could adjust, has the court movement and endurance but just seems to refuse to.
In his mind, HC is his bread and butter and to hell with red clay.
We don't usually think of Europeans that way, but a hard hitting HC American player we just assume they don't "get"red clay.
Hence Medvedev.