Hi, I started playing comp with my gf this month. I played every game with her (both support) and she got gold 5, while I got bronze 5. We then played a bunch of games again, still got bronze 5 and she got gold 5. I then tried playing games alone, I went 5-1 aaaaannnnddd… still got bronze 5. pretty sure this is a bug, can you check this out blizzard staff 
(you might want to check my gf’s account too, she never moved up or down from gold 5
-Dinner
You are not alone in experiencing this bug. Here’s a link to my post in case you’d like to read more about this issue: Comprehensive Thread Of All Top 500/Competitive Bugs. I’ve compiled a list of posts regarding similar bugs under: Incorrect Rank Adjustment. Any help in spreading the word about this megathread would be greatly appreciated.
Having same problem in diamond
I went from bronze 3 to bronze 3 to bronze 3 to bronze after only losing 2 matches and winning the rest