Honestly don't know. First noticed it about 4-5 months ago, being doing more on the bike than the gym and thought it would just go.
I can't help wondering if there's something about my desk posture, although I've got a standing desk, it's the right shoulder and that's the arm I use for the mouse etc.
Interesting, because I've also had a shoulder niggle that's crystallised since my shoulder injury healed (previous injury was posterior to the glenohumeral joint; current gripe is anterior... go figure). I actually found that part of the cause was my position on the bike (bear with me on this):
- When riding on the hoods/drops, I noticed my right elbow was pointing further around than my left (I know - I'm weird that I pay attention to these things);
- Despite rolling my elbow around, it still felt weird...
- Realised I wasn't pinning my right shoulder blade, so my shoulder was just "floating around" whilst cycling (both on the turbo and outdoors)... a bit like riding with my right shoulder shrugged, if you will...
- Now have to consciously "fix" my shoulder position when cycling...
Since clocking this, my shoulder has stopped hurting, but I still have to actively adjust my position on the bike to ensure I don't repeat it.
I appreciate it's a random issue, but you've been spending a lot more time on the bike recently so it might be something to think about...?
Hope it resolves or you get it resolved!