Hello @Alex T K,
Thank you for reaching out to the Quicken Community, though I do apologize that you are experiencing this issue.
First, I suggest creating a test file and adding the Charles Schwab account(s) to see if it produces the same issue when attempting to link your accounts. It is recommended to save a backup before proceeding with troubleshooting steps in the event that you would like to return to your original starting position. Below are instructions on how to create a test file:
After adding accounts, see if you are experiencing the same problems in this test file.
Please let me know how this goes, I look forward to hearing your response.
Thank you for providing more information.
First, I suggest that you sign out of your data file completely and then sign back in. In doing so, you will refresh the registration token for your Online Connected Services. Please follow the steps below in order to do so.
Once you sign back in, please attempt to add your Charles Schwab accounts again.
Let me know how it goes!