Could be. I've had several Subaru when they sat for a few days would not start right away. If that happened, I'd turn off the key and turn it back on. Thus cycling the fuel pump and it would start right up.
Fuel filter
Leaking Injector
Could also impact fuel pressure.
They released from the inside, if they won't pop out with reasonable fiddling from outside. The turn into place in the black piece once they are off the body. Then snap back on.