U.S. delivery firm FedEx Corp. posted lower-than-expected quarterly earnings on Thursday, hit by ongoing labor woes and the Omicron outbreak, and said second-half Ground margins will miss internal targets. Shares of FedEx fell 3.5 percent to $219.90 in extended trading. E-commerce shipments fueled revenue at FedEx and United Parcel Service during the COVID-19 pandemic, but FedEx has been less successful than its rival at translating that additional business into profit. While labor challenges began to ease in the latest third quarter, FedEx Chief Operating Officer Raj Subramaniam said volume was softer than forecast due to Omicron. “As such, we expect our second-half Ground margins will be lower than our previous expectations and not reach double digits,” Subramaniam said. Executives said volume rebounded as Omicron waned. Still, analysts called out the growing gap between the Ground operations at UPS and FedEx. “You guys are operating, give or take, at an 8 …