It is never a good idea to tell a lie to a customer. Please REMOVE the line "All of your items are available for immediate collection from your chosen Collection Location."
It is causing issues - regardless of your blue text that you customise for us further down, the customer sees the top line ... it does not make sense. In your desire to be helpful you are causing un-necessary conflict with our customers.
Please either remove or make the text customisable.
The best action would be to say they will receive an email with invoice attached when the order is ready to collect.
Thanks
Simon