It’s a know scripting error that Intuit is apparently working on.  See:

https://community.intuit.com/questions/1640087-banking-error-9999-from-wells-fargo-this-has-been-goi…

Resolution for 'bank account and issue: 'I’m getting error code 9999 when I try to download my bank transactions (bank account and credit card account).' available: Yes.

The bank account and issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the bank account and issue yourself by looking for a resolution described in the article. If it is a complex bank account and issue or you are unable to solve the issue, you may contact us by clicking here or by using other bank account and support options.

For more information about resolving issues related to bank account and in Quickbooks/QBO or to get support for the issue 'I’m getting error code 9999 when I try to download my bank transactions (bank account and credit card account).', click the link below: