Hi there, HBoswell.
Welcome to the Community. It would be my pleasure to help you get the support you need to print 3-part perforated paper successfully in QuickBooks Online.
Since you already tried clearing your cache and still unable to print on a 3-part perforated paper, I recommend giving us a call this time. One of our Phone Support Specialist will need to pull up your account and perform additional troubleshooting to fix the printing issue.
I'm adding an article that I recommend for you to reach them (you can dial the number next to QuickBooks Online Payroll):
Please reach out to me here should you need any additional assistance. The Community is on a lookout for your response.