No more than two end city portals are spawning

So i have been able to go through an end city portal the first time i killed the dragon, only to find that it led to a small island with those ender fruit things. After i realized that you can have multiple portals leading to different islands, i resummoned the ender dragon by using those expensive orbs. Now i read that you should be able to do this more than twice and have multiple portals, but after i killed the dragon for the second time, i tried to summon it again to get a third end city portal, since the second end city portal was once again a small island with fruit. The difference was this time i did not get any new portal, instead being left with two end city portals leading to almost the exact same looking island. Please address this issue as i want to have gliders