I have a bump on my shoulder like yours, although its not quite as big. I had an OTB at speed and a tree was kind enough to break my fall with the full force of my shoulder going into it.
Thought the pain & swelling would go down and it would all be ok. I didnt notice the bump on my shoulder for about a month and it was still pretty painful. I then thought id do something about it.
Went to GP who sent me for a scan at hospital. They diagnosed a cat 1/2 sprain of the shoulder (Dont know if thats the same as ACJ seperation?)
i then had 6 weeks of physio which didnt 100% cure but did improve it a lot. Physio referred me to a shoulder specialist and ever since then ive been going back every 3/4 months for a check up.
Specialist seems to think it will all be ok in good time by its self.
I’m now 12 month on after my injury, heres the good news..
Bar the first 6-8 weeks it has not stopped me riding and ive had a few offs with no further isues. Riding has no bad effect on my shoulder.
Bad news – If I do any moderate lifting above shoulder height it can play havock and my shoulder can feel as bad as it did a few weeks after the injury and take a good few weeks to return to what i now accept as ‘normal’. Got my next specialist visit end of month so will see what he says about it.