There is a known problem with reconciliation. See the thread below to see if this applies to you.
Resolution for 'bankreconcile- issue: 'Bank reconciliation error' available: Yes.
The bankreconcile- 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 bankreconcile- issue yourself by looking for a resolution described in the article. If it is a complex bankreconcile- issue or you are unable to solve the issue, you may contact us by clicking here or by using other bankreconcile- support options.
For more information about resolving issues related to bankreconcile- in Quickbooks/QBO or to get support for the issue 'Bank reconciliation error', click the link below: