Hey guys, here it is a solution, at least worked for me:
Go to edit your world that you want to put in realms. Then "play realm" in the purple(pink) button. The minecraft will export and upload. Wait in the upload screen util the message ERROR shows up. Click OK and just go to the realm and the world is in!
This bug is very sad. Every time they do a new update, this thing happens
For me, was not just the seed, the whole progress was there. I did that in the mobile version. Maybe it is different or this huge bug is doing a lot of variations to the problem.