Macbook Pro 2018 sound output won't transfer from built-in speakers to headphones

I've had a 2018 MacBook pro (13", 4 ports, touch bar, upgraded 2.7 GHz Intel Core i7) for 10 days. I haven't noticed any issues until now. Today, when I removed my headphones from the jack while using youtube or Netflix, audio output transferred automatically to the built-in speakers, but would not transfer back to headphones when I plugged them back in. I thought the problem might be that the computer didn't recognize I had plugged the headphones back in, but when I repeated the unplug/re-plug in exercise with sound preferences open, the problem persisted as the output (as shown on the screen) transferred from headphones to speakers and back as it should. When I double clicked the already highlighted headphone output to see if that would get sound to transfer to the headphones, it didn't work. Only when I restarted video after pausing for 30-60 seconds did sound transfer to headphones. The problem did not occur when using Spotify or iTunes, but in those apps, the sound faltered a bit when the headphones were plugged back in (i.e. it wasn't a flawless transition from one output to another). Any ideas?