Game crash when entering the nether portal, after restarting, all netherrack ever excavated back there

When you enter the nether for the first time in Minecraft version 18w50a, the game crashes.
When you restart the game and enter the same world where you just walked through the portal before, you spawn in the nether like usual, but every single block of netherrack that you have ever mined before version 18w50a reappears as if you had never touched the ground of the nether.