Why am I suddenly unable to use the SHIFT key following app update?

I've just updated Illustrator (23.0.4), as you do, but now the shift key has stopped working. I am unable to select multiple items with it OR scale.

Any ideas as it was working fine beforehand?

Thanks

macOS Mojave
10.14.5

iMac (Retina 5k, 27", 2017)