To reproduce.

Open Minecraft, wait a few seconds for the game to load your MC account. And it crashes, same thing with the pause menu.

And as you can also see with the other screenshots, it doesn't crash if account didn't properly load

Edit:

If the profile button loads. It crashes

I noticed that when I have a resource pack that changes the ui, the profile button isn't there. My account loads, it doesn't crash. And on my first assumption I thought it was the account loading in.

But I think it's the profile button, loading on offline mode that crashes Minecraft.

Because everytime I take the resource pack off, and the profile button appears it crashes

-Turning the internet on fixes the problem temporarily. But the problem still occurs. After a while

• Problem doesn't occur when internet is on
• Problem doesn't occur when you've recently turned off internet 
• Problem does occur after a while of being offline
• Problem does occur everytime the profile button appears (Main Menu and Pause Menu)