If the cart has multiple line items of the same product (auto merge is not enabled), then the checkout registration forms only show up for one line of the product line items.
The attached patch solves the problem, which basically uses a counter for all the registrations instead of on a per line item basis.
Closed: outdated
2.0
Registration Pane
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It's likely this issue predates Contrib.social: some issue and comment data are missing.