It’s a script error. ¬†You must report it to QuickBooks.

See below.

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

Resolution for 'bank side issue: 'Lost connection to my bank for the past 5 days. Nothing has been changed on bank side. Not sure why the connection is lost.' available: Yes.

The bank side 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 side issue yourself by looking for a resolution described in the article. If it is a complex bank side issue or you are unable to solve the issue, you may contact us by clicking here or by using other bank side support options.

For more information about resolving issues related to bank side in Quickbooks/QBO or to get support for the issue 'Lost connection to my bank for the past 5 days. Nothing has been changed on bank side. Not sure why the connection is lost.', click the link below: