Just to minimize the chance there's just some software-related issue try booting up your S7 into its Safe Mode. If both channels are working while in Safe Mode then it's a matter of narrowing down what app might be the culprit. Have you installed anything that corresponds to the approximate time this problem started to occur? Also, it might not be specifically an app that's the issue but rather a recent update to an app. If you start up the Play Store app, go into the hamburger menu (three horizontal lines) in the upper right, tap on 'My apps & games', and see what's listed in the 'Recent updated' section.
Another possibility is there's just some lint or dirt that worked it's way into the headphone jack itself that's creating the problem. As you mentioned your headphones work OK elsewhere it's probably safe to eliminate the plug on your headphones so focusing on the jack inside your S7 you might want to try to just gently use a can of compressed air to blow it out. Stress the word 'gently' don't spray the air directly into port opening by holding it too close (and if it's the type with one of those narrow straws to concentrate the air flow don't insert that straw end into the jack). Another option is to pick up an aerosol can of electrical contact cleaner. They're available in most computer/electronics stores, a lot of hardware stores, and online retailers of course. A very small squirt is all that's necessary, less is better than more. (Note they're typically a mix of all kinds of multi-syllable chemicals so keep that in mind but they do work pretty well -- evaporates quickly and leaves little residue.)
This might help explain things in a pictorial way.
If you look at the plug end of your headphones, there should be three metal contacts separated by two plastic insulators -- the shaft part is the ground, middle ring the right channel, and the tip end the left channel. Fortunately for all of us that's more or less the industry standard that all the manufacturers used.
Below is a common headphone jack, it's exact appearance varies (so the jack in your S7 doesn't look exactly the same but it's an accurate representation).
There are metal contacts in the jack body itself that correspond directly with metal contacts on the plug (ground, right channel, left channel) so when your headphone plug is pushed all the way into the jack the metal contacts match up, and that's how the audio signals from your phone flow into your headphones. Going by your description it sounds like (pun intended) that the right channel connection is the problem. Hopefully it's just lint/dirt inside the jack. A more serious issue is if you do need to replace the jack module itself. See this ifixit link (step 14) for better details: