I posed a similar question earlier this week under “Possible nerve impingement..”
It’s been that way for a couple of years for me. I first noticed it after a BJJ injury involving a very sudden very hard distraction of my shoulder. It doesn’t seem to limit my movement. However my shoulder does just have a faint uncomfortable feeling all the time.
Mine does seem to be improving ever so slightly with scap and t-spine work and a bit of conscious effort when pressing heavy overhead or doing gymnastic movements.
Is it possible you were just unable to flex it earlier and only just noticed this now?