Invoice download link inconsistency

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I have a cart that has the latest VM 2.020b and Joomla 2.5.11 installed. I have the PayPal and Authorize.net gateways configured. I've tested both in Sandbox mode and have been able to get the digital download links to display in the invoice and online account when paying through both gateways in sandbox mode.

I switch to live mode and about 1 out of 4 order invoices and account contains the download link. There is no pattern that I've identified to why it works on one order and not the other. I've even used the same products to eliminate product discrepancies.

Any ideas?