See picture attached.
Thank you for sending in the question, and apologies for the delay in responding! This post seems to have slipped through the cracks.
Unfortunately, I don't have a whole lot of great news for you here...Currently combination charts cannot be sorted like column or line charts. So you would have to consider one of those charts as alternatives if sorting is mandatory.
If your chart was a bit different you could consider using Org Ref Codes to sort your data in a specific order. But in the example chart you have shown--this wouldn't work as org ref codes can't be applied to date fields. If your chart was based on month name rather than a specific day date this could be an option.
Anyway, sorry for the spot of bad news. Please let us know if you have any questions or concerns.