I get it as well , i just set the fps_max at 64 and left it there , seems to be working fine on that setting , fps shows to be 63 , but the game plays steady , which is all i really care about , though i dont recall having this behavior untill recently , unless i just hadnt payed attention to the fps , and untill recently i kept running the old 6.22 , till i decided it was time to upgrade to 6.31 , i'll do a reinstall one of this days on another drive and see if it's the 6.31 update that caused it , though i can live with having the fps_max at 64 rather than 60.