Cooking sirloin steaks with Anova sous vide gave me leather tough steaks I'm new to the Anova sous vide machine and have successfully cooked tenderloin steaks beautifully with the device. 
The other day I saw nice thick sirloin steaks in the supermarket which I then cooked at the same temperature as the tenderloins but for 15 minutes more (This was all using the temperature and time guide in the Anova app so from 45 mins for tenderloin to 60 minutes for strip as there are only guides for porterhouse/ribeye/stri/tenderloin)
The one thing I did differently is I forgot to season the tenderloins before I sealed the bag. 
Seasoned before I seared and sat down to enjoy my tender juicy steak and it was like eating a piece of leather. As in it was totally uneatable. The temperature was spot on but the chewiness was horrible. 
One bag did end up getting pushed around in the pot and was touching the Anova for most of the sous vide time but boh turned out the same. 
Any helpful advice on why the steaks turned out so tough?
Thanks in advance!
If you think of tenderness on a scale, sirloin and tenderloin are nearly on opposite ends of the scale. Sirloin, in general is not a tender cut of meat.  Your result has little to do with seasoning or location in the water bath...or even cooking method. Sirloin is a lean and tough cut.  Often sous vide can be used to make tough cuts of meat more tender, but sirloin doesn't really have the collagen or connective tissue that will break down like, say, a short rib.  If you like the tenderness of a tenderloin, you will never match it with a sirloin.  Don't blame your circulator, it is akin to blaming your stove when things don't go well there.