In the first picture after be killed by the dragon during the fight and go to the overworld and enter to The End again there were a lots of dragons. ( if you put your monitor brighter you will see like 5 dragons). I left the game and i entered againg and this time there were 2 of them (sometimes there were more dragons and sometimes less) so I decided to do this until there was only one dragon.

After beating the dragon there were a couple of them again. Then after defeating them once more there were 2 end gateways. 

Now there are three of them again.

It happens everytime you enter  to The End.

This bug is reported since 19w09a at least.