Galaxy S6 :: Why Audio Coming From Headphones Muffled

An odd thing has been happening to my Samsung Galaxy S6 recently, and I have had no luck at resolving this issue so far. When plugging headphones or any other auxiliary cords into my phone to listen to music, all of the audio coming through the headphones is muffled, like it is playing from behind a window. I have done many things to try to resolve this issue, including trying different headphones and restarting my phone, but no luck. It was only when I tried something else that I concluded that this issue is not hardware related. When I used a 3rd party music application (in this case Spotify), the first second of whatever audio is playing comes out perfectly fine, but very quickly switches to the muffled audio. I have also figured out that only while on Spotify can I temporarily prevent this issue from occurring by opening up the default music app on my S6. This somehow changes the already playing music from muffled, to regular.