By Lisa Baertlein LONG BEACH, Calif., Feb 27 (Reuters) – Collapsing ocean shipping rates are not all good news for U.S. retailers, who paid as much as $20,000 to move a container of goods during the worst pandemic disruptions, as they now are bracing for delays due to plummeting demand. Carriers like MSC and Maersk are trying to prop up prices by canceling voyages and that could spark a new round of cargo delays as containers get bumped from one ship to the next, experts said ahead of a major U.S. ocean shipping conference in Long Beach, California, this week. The event, called TPM23, marks the unofficial...