I have both Kyogre and Groudon in My Ultra Moon but I go through the Red portal with the 2 rings and has the aura coming of it and it gives me other legendary Pokemon.
Why does this happen? I have tried for like 20 - 30 times but I havent got it. Why is this?
Even with Groudon and Kyogre in your party, you're not guaranteed to encounter Rayquaza every time you enter the portals, so just keep going through the wavy portals. It takes some time, but eventually you'll find one.
Rayquaza isn't guaranteed to come out of a legendary wormhole.