I agree the emoji issue is a little overblown, but I think "almost unusable" could be appropriate.

On a phone, the synergy of autocorrect and fat fingers is a delicate one, and even small changes can really upset the typing experience.

Samsung once updated the keyboard on my phone, and the different visual cues and behaviour completely threw off my muscle memory and made typing very difficult.

Even the autocorrect mode being wrong on an email input can be annoying, so a whole app acting up would be even more unpleasant.