Had similar issue, I was using test P in vial no pip, switched to the same test P but in amps and got pip and the pin area is red every time, I have more boxes so I'm just gonna finish it and continue with the rest, hope was only that box. Same needles, same technique, same everything. I don't see any reason for this.
However, been using tren a from vials and amps and no pip with any of those.
I did change the test P dose though from just 30 mg a pin to 100 mg, not a big deal anyway, is very mild, but never felt any pip or nothing before.