I went to a sports medicine doc to have him look at something similar.
I’ve always got some extra chaffing on my left side. It can go from not noticeable to I feel it after every ride depending on shorts, saddle, and mileage.
A few years ago the area a swelled up. It turned out that I burst a blood vessel near my left sit bone. It was painful to ride but an ultrasound showed nothing serious. After a couple of weeks of recovery and wearing two pairs of shorts I was back to riding.
After that I started the long experiment of trying every kind of saddle as well as trying different bib shorts. I found some saddles that worked better than others and I also found that I love Assos shorts more than any others.
After a lot more analysis I’ve come to the conclusion that I sit crooked on the saddle. If you look at your friends in group rides you’ll see that most riders actually side left or right of center. Note that the seam of bib shorts hardly ever lines up with the center of the saddle. I sit most comfortably to the right which makes the left side rub more. I also don’t sit perfectly square - think about the pelvis being perfectly perpendicular to the center line of the bike. There is some degree of offset that I find most comfortable.
Solution: I force myself to sit as square as I can on the saddle. It feels odd at first but I’ve gotten used to it and all my left side abrasion/pain has mostly gone away.
For further research one can google “perineal nodular induration” or “cycling third testicle”. It has nothing to do with actual testicles but - WARNING - one may find the photos to be graphic or gross - definitely medical.
Really it’s just a fatty mass that can develop in the saddle area from the constant abrasion and in super rare cases it can get large. Probably lots of cyclists have small ones they don’t even notice and never treat.