All block textures missing in flat world

All the textures are missing in this world, so blocks are either pink or black.

this bug happened after I left the app without closing it and later came back and found these weird colors. The world was a flat world that had been previously messed up with another glitch that caused flat worlds to not be infinite. 

After leaving the world and coming back to it, it was fine and all the blocks had their textures again.