This has been an issue for at least a couple of years. Worlds from around 2016 or earlier cause the game to crash on "Building Terrain". I tried to load it on Android and received the same bug. This has been a problem with multiple different older worlds in the past.
To reproduce:
Try to load a world from an older version of Minecraft Pocket Edition in modern versions - It seems to be worlds prior to around version 1.0.0 that have the problem - a copy of my world from January 2017 loads fine, but a copy from December 2016 crashes.
Edit: Interestingly, a world from earlier in 2016 loaded successfully, which was a pleasant surprise. Doesn't seem like all worlds are affected by this?
Edit 2: I suspect this issue has been significantly improved from the issues I was having a while ago. Most of the worlds loaded successfully and only one failed. I wrongly assumed from one world that it was still a bug affecting all old worlds (as it was before). But still, one world out of six crashed, which is still probably an issue.
Comments 3
Resolving temporarily as Awaiting Response. Could you export a copy of an affected world and add it to your report? If it exceeds the file size limit, you can upload it to a file sharing site (e.g., OneDrive) and link it here.
This ticket will reopen automatically when you reply.
Cleaning up old tickets: This ticket had been set to 'Awaiting Response', but has not received a response from the reporter (~3 months+) so is being closed as Incomplete. If you feel this is still a valid issue then please comment, or create a new ticket following the Issue Guidelines which includes steps to reproduce the problem.
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Resolving temporarily as Awaiting Response. Could you export a copy of an affected world and add it to your report? If it exceeds the file size limit, you can upload it to a file sharing site (e.g., OneDrive) and link it here.
This ticket will reopen automatically when you reply.