If their historic allocation was similar to their current one, it's no surprise; its a very bond heavy vehicle and bonds over the last decade have had basically non-existent interest rates.
Most 529 plans are target date funds timed to when you start college. So it lost a lot of money when the pandemic hit and then moved into its very conservative phase as the market recovered. It also took a big hit in 2008 though I was only a few years into investing at that point.
