Well I don't know if it happen in pc because I am good with mobile control and play ark mobile but for me rex is soo much easier then taming spino you just need a high place where rex can't reach you and hit him with treanq arrow or tranquilizer dert until it got unconscious then just feed prime meat it won't take lot narcotic 10 is enough for me I didn't even needed narcotic I tamed a mex level rex without narcotic