If a checkout sheet kit is causing issues, could it indirectly lead to Shopify error 2?

Yes, a poorly implemented or incompatible checkout sheet kit could indirectly lead to Shopify error 2. If the kit interferes with the correct transmission of payment information to the gateway, or if it incorrectly parses customer details, it could result in the gateway being unable to authorize the payment, thus triggering error 2. This is especially true if the kit modifies fields or processes that the payment gateway relies on.