P: Select and Mask: keyboard shortcuts no longer work (macOS)

In the 'Select and Mask' workspace in Photoshop CC2019, the keyboard shortcuts for switching tools/adjusting brush size (eg 'z' to switch to zoom tool, '['&']' to adjust brush) appear to no longer work. This is actually quite frustrating, as habitually tapping a key to change a tool does nothing, and the wrong tool then often ends up being applied.