This happens from time to time. Most likely, your designer got sick, a family member got sick, or they went on vacation. The designer who stepped in is on the same team as your regularly assigned designer. That means they share the same Quality Review Manager who can alert your temporary designer of any important considerations.
In the event that your designer is promoted (yay!), we will notify you in advance. I know you will be sad, but sometimes it's best to let your pickle find another jar of brine.