This can be caused by a damaged data file, Janie2019.

Let's run the Verify/Rebuild Data Utility tool. Before doing so, let's review if your term is set up properly.

Here's how:

1. In the upper left corner, select Lists.
2. Click Customer & Vendor Profile Lists.
3. Choose Terms List.
4. Find your Net 30 term, right-click it and select Edit Term. 
5. Make sure the parameters are set (for a Net 30 term, the Standard bubble should be selected and in Net due in should say 30).
6. Click OK to save your changes.

 Pull up the invoice once again. If you're still seeing the past due stamp, I suggest running the Verify/Rebuild data utility tool.

Here are the steps:

1. Go to File, and then Utilities.
2. Select Verify Data. 
3. QuickBooks will ask to close all windows. Click OK.
4. The program will prompt you to create a backup before rebuilding the data. Click OK again.
5. On the next window, select Options.
6. Click Browse, to pick where the file should be saved (you can save it on your desktop).
7. Choose No verification, and click OK to continue.
8. Pick Use this Location, and then select Next. 
9. Click Next again, and save the file. 
10. Once the backup is finished, the Rebuild will run.

Feel free to leave a comment below. Have a good one!