QB Issue Resolution:

Check first in your Windows settings, it may have changed there and you may only need reset it. Quickbooks has no date formatting of its own but relies on Windows or other OS format.

Resolution for Issue 'since updating to windows 10 at the end of june the date layout has changed to American format i.e. 07/01/2016 for 1st July instead of 01/07/2016' available: Yes (Solved).
Source: Intuit Community forum.

since updating to windows 10 at the end of june the date layout has changed to American format i.e. 07/01/2016 for 1st July instead of 01/07/2016: this 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 issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

Support for American format
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Error Recovery for American format [Canada]
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