This holds not true. Actually Kanto (and Johto) bosses have been resettet during the last 4 weeks. However this excluded some bosses like Jessie & James or Koichi.
Well but back to Topic:
For fighting Naero you need to fullfill the following requirements:
- Requirement : 6 Pokemon Lv 100 - 201 hours playtime (source: https://pokemonrevolution.net/forum/viewtopic.php?t=9593#at_0 )
If you fullfill the above named requirements and still can't battle him (+ you haven't lost vs him during the last 2 weeks) we wont be able to help you. You need to wait for a member of staff to may fix this.
BR
Gami
I do have the matched requirments, i will post a screenshot of it in a bit , and he has been down for a month, that's when i lost to him.