MacOS – Why did the emoji and predictive input stop showing up on Touch Bar while typing in WhatsApp desktop Mac app on MacBook Pro

The first things I would do are reset your NVRAM followed by resetting your SMC. See below for further info.

Resetting the NVRAM on Late-2016 MacBook Pro models

Older Macs had what's called Parameter RAM (PRAM), newer Macs use Non-Volatile Random-Access Memory (NVRAM). To reset the NVRAM on all Late-2016 MacBook Pro models (with and without Touch Bar) follow these steps:

1. Shut down your machine. Yes, a full shut down, not just logging out.
2. Press the power button and then immediately press the commandoptionpr keys.
3. Keep these keys pressed down for at least 20 seconds!
4. Let go of the keys and let your Mac reboot normally.

Note 1: When you log back in you may need to readjust some of your system preferences (e.g. speaker volume, screen resolution, startup disk selection, time zone information, etc).

Note 2: These steps will also work to reset the NVRAM (or PRAM) for all Macs. However, the late-2016 MBP models actually required the commandoptionpr keys to be held down for 20 seconds, while earlier Macs did not require this, but doing so does not cause any problems either.

Reset the SMC

Your MacBook Pro has a system management controller that can easily be reset. To do this on your particular model, follow these steps:

1. Shut down your computer
2. Keep the power cable plugged in.
3. Press at the same time shiftoptioncontrol (on the left side of the keyboard) and the power button
4. Let go
5. Turn your computer back on with the power button.

Let me know how you go after doing both resets.

Must have been a bug. Haven't experienced again.