Maybe the actual Windows settings got returned to default. Multiple displays in Windows 10 are controlled by the OS not the GPU Driver. Not by any means saying it can't be a driver issue but I would check out the Windows settings to make sure it is set to extend the display to the second monitor still. If that doesn't work, do both monitors work by themselves on either port?
Open the settings gear in the start menu then go to display to check if the 2 monitors are set right or not.