This happened to me three times now ever since updating to the latest firmware.
I'll try to go back my library but nothing happens. Clicking the library button on the top left of the screen does nothing, and after a while, that option just completely disappears. The options aren't also working. They act as if I'm already at my library but the screen is still displaying my book, and I'm even able to switch pages. The only way I can get out is to restart by pressing the power button until the restart option pops up.
It's not that big of a deal, but it is annoying when it happens since restarting e-ink devices takes a while.