I am having the same issue, and yes, I can confirm that this is still occurring as of 1.14.60. I have just tried to upload my world to Realms from the XBox One, and get the same problem as above. The messages state that the level export finished successfully, and then tries to initialize the world, but get the error message: " Failed. An error occurred."
My answers to your questions above:
1. I cannot find the version number for the save game, but my xbox load screen says v1.14.60, and I just saved the world this morning (19 April 2020).
2. The error message as detailed above.
3. Uploading from XBox One S
4. No add-ons
5. World says 575.7MB
6. Tried this. Still awaiting the outcome... [Edit]- Unsuccessful...
I just wanted to update this, in case anyone else is having the same issue. I have just successfully managed to upload my world to Realms. I suspect (although cannot prove) that my poor connection speed was the main cause of the problem, so I tried uploading at a time when I thought the local internet traffic might be quieter, starting at around 6am.
As with previous attempts, the level export finished successfully, and then the attempt to initialize the world went on for even longer than previous attempts, which made me hopeful that it might be successful this time. It eventually competed successfully about 30 minutes ago, having taken approximately one and a half hours to initialize a 575MB saved world.
I guess the moral is to pick the right time and be patient!