I experienced the same thing when I first started cruising, which I put down to something related to test propionate (I believe GF or Guido suggested it'd be to do with the solvent used), and also again recently when having to cruise on sus250 in place of test E.
As GF said above, it's likely nothing to be concerned with. I wouldn't be surprised if it's your body having a mild reaction to something in the blend (one of the solvents/oil used) and given you're now using a lower concentration blend, there's perhaps MORE per ml of whatever's irritating you. This is pure speculation mind you, as it kind doesn't make sense (would only really indicate the oil irritates you, if these symptoms persist)
That being said, you're also sticking 1ml into virgin muscle (given it's been so long since it was last pinned), it's a decent amount of oil into a fairly sensitive muscle (IME at least. Always got corking in glutes). Likely just explanation number 1 from GF.