Inserting postmeta doesn't always work...only sometimes

We have a theme page template that's basically a glorified contact form. It takes user input, and we have it assigning the lead to a round robin lead system, which picks a user and gives them the lead as a CPT entry, and emails the lead to the sales person assigned.

The problem is it only works sometimes. In our testing, we haven't been able to reproduce a "bad" entry, but have seen a number of them come across that have a post created, but the meta data isn't present in the CPT entry.

We've tried regular postmeta inserts, but are more recently trying a batch insert of the postmeta information through a query instead of WP functions, thinking maybe MySQL was getting bogged down with too many queries at once (one for each custom field). Apparently that wasn't the case, as it's still occasionally happening.

At this point, we've spent weeks chasing this ghost bug, involved multiple developers, and burned countless hours. If anyone has any brilliant ideas, it'd sure make my life a lot easier.