Ok I know people here have said they use those and I got a buddy that uses those as well. I have never heard of a problem with them except when concentration is high. I got a buddy that did some 500mg/ml stuff mad man or mad max...i don't even know what it is and he has to get that lanced this coming week. Possibilities all have pretty much been said but I will recap.
1.A fluke sometimes this happens who knows why, you didn't get an infection and you had/have a lump that will most likely go away. I'd still use that bottle
2.300 mg /ml is too concentrated, I personally would mix that with something else...or dilute..honestly if I ran something that high I would fill the dart up with something else that is planned. You use pins though. you could always put 66 units in and then dilute with 34 and have 200mg/ml. Kinda sounds like more trouble than its worth though but if you have 10 bottles of this stuff or have your budget max out it may make sense.
3 The solvents are causing inflammation, again guessing I don't know how to make stuff that high if its beyond 2/20. I typically just buy it, but its a google search away. Really I just buy everything these days I don't do brewing anymore, I just don't use that much.
4 Someone said you could switch esters to cyp, that could be helpful, I personally would not though but that is me. I mean I would/will switch to cyp....eventually.
I would just try it again in a larger muscle group and see how that works out. Save the tri's for something less concentrated. I think pretty much everyone thinks localized muscle growth really isn't a thing. If it was I'd have huge legs and I do of course but when I take pictures they look a lot smaller for some reason.