When my keyboard is open in a Whatsapp chat, and I press the green microphone to record audio, the 3 words on top of the qwerty part disappears.
After recording audio it is still missing. Pressing a letter then brings it back.
Just a strange bug, not sure if it is a Whatsapp problem but please test on your phones and see. My friend's phone does the same, and it is a different phone.