The bug

When trying to join the attached world, the loading screen will get stuck at 100% and won't open. The world has been created in 19w08b and only been opened in that version.

Additionally, the following error messages appear in the game log file (full file attached):

[12:00:44] [Server thread/WARN]: Wrong location! (-1, 2) should be (0, 2), aqy['ClickDetector'/275, l='Redstone Testing World', x=-0.70, y=-200.00, z=39.56]
[12:00:44] [Server thread/WARN]: Wrong location! (-1, 5) should be (0, 5), aqy['ClickDetector'/546, l='Redstone Testing World', x=-0.24, y=-200.00, z=86.89]
[12:00:44] [Server thread/WARN]: Wrong location! (6, 8) should be (5, 8), aqy['ClickDetector'/1314, l='Redstone Testing World', x=96.08, y=-100.00, z=142.35]
[12:00:44] [Server thread/WARN]: Wrong location! (5, 8) should be (6, 8), aqy['ClickDetector'/1625, l='Redstone Testing World', x=95.70, y=-200.00, z=135.23]

The world includes the data pack "BlingEdit" by SethBling, which is where the ClickDetector entity seems to come from. However, "BlingEdit" has been disabled before the world has been saved the last time.

I waited for quite a while (over 15 minutes), but nothing did happen, so I needed to kill Minecraft via the task manager.

To reproduce

1. Try to open the attached world
2. The loading screen will get stuck on 100%

Workaround and conclusion

I went ahead and deleted all entities from the world manually via the region files. After this, I could join the world without any problems. This proves that there's something wrong with these entities being loaded. As their y position is negative, I believe that in this snapshot, entities don't get properly killed by the void. Further testing required!