The start of trading on the Chicago Board Options Exchange CBOE +0.52% was delayed Thursday due to system problems, according to the exchange. The biggest U.S. options exchange by volume said in a system alert that some of its customers were having problems “downloading” information from CBOE early Thursday, and at least one other exchange stopped sending business to the CBOE during the outage. CBOE intially planned to reopen at 10:15 a.m. ET and then again at 10:20 a.m., but later delayed trading with no estimate as to when the exchange might get up and running, according to notices sent...