The kind of QuickBooks behavior about missing vendors and customers can be fixed by some basic troubleshooting steps.
Let's try using a private browser or incognito window as an initial step to fixing this issue. This will eliminate any browser history that may cause a glitch inside QuickBooks. You can refer to the following keyboard shortcuts below:
Google Chrome: Ctrl + Shift + N
Microsoft Edge: Ctrl + Shift + P
Firefox: Ctrl + Shift + P
Safari: Command + Shift + N
If it works, close out the private window and clear the cache on the regular browser. This will remove previously-stored browsing data that might have caused the issue. Otherwise, you can try other supported browsers to help narrow down the cause of this behavior.
I'm adding this article for more information about managing vendors and customers in QBO:
Since you're new to QuickBooks Online, let me share these easy-to-access articles, webinars, and video tutorials that will help you in familiarizing the different tasks, features, and functions of QBO. Below are the following:
I'll gladly help you show the vendor list in your QuickBooks Desktop (QBDT) account.
Before anything else, I'd like to know if there's an error shown on your end and if you're referring to the missing Vendor Lists tab or the actual lists of your vendors.
In the meantime, we can run a file doctor from the QuickBooks Tool Hub. This will help fix common errors such as missing tabs, names, items, etc.
Keep in mind to never use QuickBooks File Doctor on a file that's been rebuilt recently. Feel free to follow the steps below:
Close your QuickBooks. Then, download the most recent version of QuickBooks Tool Hub and save it on your computer.
Open the file you downloaded (QuickBooksToolHub.exe).
Moreover, you can Verify and Rebuild Data in QBDT to see if the origin of the issue is in your company file. However, let's first save a backup of your company file.