MED Cancellations

So a couple of weeks on Monday, I was riding MED Mainline Inbound 712 from & while the 🚆 was traveling between Riverdale-Kensington/115th Street, the conductor said that this 🚆 will go local from 111th Street (Pullman)-59th Street/UChicago due to 214 getting cancelled due to a derailment but said that the 🚆 will run express to Museum Campus/11th Street after departing 59th Street/UChicago & I wanna know, what was that derailment all about?