Tried converting again today, went a bit better than last time. Last time a bunch of the blocks around the piston doors were out of place as well as the doors not working, this time I'd say maybe half of those block errors, but everything with pistons is still affected. Chests seem fine, I left my player above ground this time so when it converted I didnt fall through the map. I have one room that sorts items and has a LOT of item frames and chests/redstone chests/hoppers and droppers, I don't know if thats causing my issue but when I try to go down the hallway and I get near that room, the game just crashes back to dashboard. If I boot up the game after the crash, I spawn in underwater, about 20 blocks above where I was when it crashed. Weird. Hope this helps somehow
I've been suffering from this problem for a long time too and was finally able to transfer my world, though everything made with pistons is broken and when I walk up to a certain point the game crashes. When I first spawned in I fell through the world and died as well, and when I tried respawning it happened again and again until about the sixth time, when suddenly it put me in the normal world spawn. Very close, I'm sure you've almost got it!
While the crashing error seems to be fixed and it transfers my world every time, my 3 block high pistons doors all malfunction, with the middle piston not seeming to receive power at all. Some more complicated piston contraptions and doors also malfunction, including an item sorter I spent days upon days on. In the item sorter room there are chests and item frames for most items in the game, and in the corners of the room where an item frame sits in a corner right beside another item frame on the next wall, all of the item frames in the corners have come off the walls as well as the items within the frames. I really want to switch to the new version and enjoy realms but this is just killing it for me.