” The NYSE has reportedly also told floor traders the exchange had to suspend trading due to an error with a systems upgrade that was rolled out before the market opened on Wednesday.”
This is even worse. The proper way to do this is to install the upgrade on Friday night, and do a full day of system testing on Saturday. If there are problems, you’ve got all day Sunday to roll it back.
This is what all the banks do, from bitter experience.
Just about anybody. Not doing that is complete idiocy, if that’s what really happened.