I had the same problem after installing QB for Mac 2019, the voucher style checks were not printing anything on the check stubs.  Today, I entered a check To Print, then selected File: Print Check.  The window that opened had a choice of three styles of checks on the bottom left of that window, the second radio button was Voucher Style.  The preferences: checks window lets you select what you want printed on the voucher stubs, but to get it to print Voucher style, you have set it up through the File: Print Check window.