With a text frame selected and the Text Frame panel open, I typed a number in the Left field, then pressed the tab key, which moved the focus to the spin buttons for the control (expected behavior). I pressed the tab key again, expecting the focus to move to the next field (Right), but this didn't happen. Instead, all controls and panels disappeared. Pressing the tab key again brought them back, however the focus stayed on the spin button. It never moved to the next control. Pressing shift-tab would occasionally move the focus back to the preceding field.
I've had this happen on two different macs, one running Sierra , the other running High Sierra. I've tried with multiple documents on each machine with the same results.
Hope this makes sense.