Original world crashes during generation, backup from a months ago works fine

I have a superflat world that I've created in MCPE v0.9.0 (or whichever version superflat was introduced). I have an interesting problem. I am using v1.4.3. Every time I try to open my world, the game crashes during world generation. I've made many backup copies of this world. I have a copy from around January of 2018, and I can open it in 1.4.3 and it works, but the original world does not work. So the problem may be caused by something that was saved to worlds in versions between January and now. I also have "invisible" resource/behavior packs. Meaning, they appear in the lists under the world options, but they do not appear in the storage management list. I cannot delete them or view them in the main options menu but I can see them in the list on the world menu. I'm not sure if this is related, but any info helps.

Device: iPhone SE 64GB &- iPhone 256GB

OS: both run iOS 11.4

MCPE: v1.4.3

 I have a video link: https://youtu.be/zIqPp2_05X8

Notes in video: I show how some resource packs are visible in only some lists.

I also show how I can open an older version of a world but not the original. In the world that opens, I bring the player to the current location of the player in the broken world.