When 1.2.1 came out, I decided to see how much better the server connection got. I tried on my PC first, the game never fully started up. The Mojang and Minecraft logo would pop up on the loading screen, but the game would simply crash right before it finished. When this happened, I went onto my Xbox One to see if it would happen on there too. Nothing went wrong. Then I checked Minecraft on my phone, nothing went wrong on there too. I decided to wait until 1.2.2 came out to try on my PC. It still didn't work.
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Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-19903.
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I got this fixed by uninstalling and reinstalling the game, although it was still broken after the first 2 reinstalls.