It took me almost 4 weeks on my Rogue.
Got stuck at 18 on week 2. Needed 19 for next story quest. Ran a combo of about 20 dungeons and BGs and got zero renown. Then weekly reset hit and I got to about 30 renown after 2 or 3 days with hardly any effort. Then it stalled again. Following reset it started coming in again and easily hit 40 at that point.
Either it’s bugged or it’s very RNG based and some have good luck and some have bad luck.