Top panel won't display with a dual screen setup, error message when changing tags

I only get a top panel on the primary display, and when I try to change tags on the secondary display, the line

s.top_panel.visible = not fullscreen (was it line 25 in the original code?)

returns this error: "attempt to index a nil value (field 'top_panel')

Any ideas on how to fix this? Thanks!

Running latest Awesome WM version (4.3) on an Ubuntu 18.04.