More likely you had unticked the :
Release Audio Driver when Application is in the Background.
(found in Studio Setup / VST Audio System)
Then Cubase still has a hold on the driver and Foobar2000 can’t play while it’s open.
Well some can do it without that setting and some can’t, depending on the audio driver, if it is multiclient or not.
Most of us has experienced it one time or another, so no problem, just a setting that has to change to fit the driver and your needs.