Unable to open 1.12 world in 1.13

Hello,

I have a world that works in 1.12.2 won't open in 1.13 pre-2. I have been googling this for a few days, I could not find a similar bug reported/

I would like to recreate the basic structures from my 1.12.2 world and load them in 1.13 using as much 1.13 features as possible.

Here is what I did..

In 1.12.2:

-recreated the world using the seed

-set the world spawn to where it was before (about 5000+ blocks away from the original world spawn)

-used structure blocks to add a few of the original world structures around the new world spawnpoint. some are complicated with other structure blocks, entities, portals, end gateways etc

-reset my repsawn point with the /kill command

-saved and quitted

In 1.13 pre2 [_edit - originally wrote pre1_] I am unable to load the world. It seems to hang at "Loading world" and the console stops at:

repeating indefinitely. I need to close minecraft from the task manager, and there is not crash log created.

Please find attached. Thank you for your time!