The 788 has only 5 rows in business, so fewer business class seats. There is a small risk that the airline may downgrade the plane on the route, either for load or other issues, but it is likely a very small risk (but higher than normal during covid times). If that happens, the system will likely move the business class occupants to the same seats on the smaller plane, so rows 6-7 will have no equivalent J seats on the 788. Thus, we may end up with no seat assignments or a middle seat assignment. But as I said, a very small risk...