The problem arises due to the slow claiming of the onchain side of the swap mechanism. As a result, the swap service is generally forced to pay up the hold fees. Even if a "reasonable" grace period is set at the swap service, the onchain side of the swap can delay the release of onchain. To combat this issue, the swap service would need to issue a separate invoice for the hold fee for the actual swap payment. Boltz protocol supports a separate mining-fee invoice that is issued after the invoice is "locked in" at the swap service. However, a combined mining-fee+hold-fee invoice would have to be issued at the same time as the "real" swap invoice to mitigate against the problem.