Well i dont think its a bug. THe medal says REACH and not HAVE friends level 6. So you have to reach level 6 while season is active. At least they reduced number of people you need to finish this time. Last time you had to get 15 people in total if im not wrong/ Its so *ed.

Ill just do it once for the CPs,tickets and ninja frags. And there is an easy way to do it. Make 3 new accounts. I dont think any leveling is needed. Add them to the friend list and just water the wishing tree and assign commisions from the ninja task room every day. This way you will get 4 points per day. I know it *s to do smt like this but if you dont have any friends level 5 or lower there is noting else you can do.