Thank you for taking the time to visit the Community to post your issue, although I apologize that you haven't received a response.
I would recommend running the Validate & Repair tool on the data file from the File menu > File Operations > Validate & Repair option.
In the Validate File window that opens, click the top box to "validate file" and then click OK.
When the validation completes, a data log will open in Notepad, please let us know if any errors or issues are found/repaired, and when ready close and re-open Quicken.
Please let us know what you find!
-Quicken Tyka
After adding an account, see if it saves the password in the password vault (you will likely be prompted to create one first) in this test file. After successfully saving, close and re-open Quicken to verify whether or not the password remained saved in the vault from the test file. From there, you can then switch back to your original file.
Follow the steps below to switch files:
Quicken will list the most recently opened data files, with a checkmark next to the file you are currently viewing.
Let us know how it goes!