Facebook – Only some of my pages show up when I try to join Group as a Page

I manage 3 different Facebook pages, but when I try to join a group I can only choose 1 of them. I have checked the settings and I have the Admin role for all pages. I also cannot see any pattern in it based on number of likes and age:

  1. Page 1 – 8 years old with 10.000 likes (cannot join)
  2. Page 2 – 3 years old with 50 likes (can join)
  3. Page 3 – 2 weeks old with 2 likes (cannot join)

Anyone have suggestion for how to fix this issue?