Injection onset delay?

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I've now done over 40 injections. Of all the injections, one was a complete miss, not even a chubby.
A couple of times I had a delayed reaction that took 20-30 minutes before I was able to get erect.
Until last night, except for one obvious miss, all the injections I have done have resulted in 85-100% solid erections that last 1+ hours.

Last night I injected, but never got fully hard. That didn't stop me. As I gave my wife Oral sex until she came.
I then forced blood into my penis with the help of cock ring. Producing 60% erection, just enough to allow intercourse that lasted maybe a minute, then I came.

Seems to me I missed the injection spot last night, but the residues caused a limited erection. Is that even possible?

What I'm asking is I've done over 40 injections, one was an obvious miss, not even a chubby. All of the other injections (except last night) have produced good solid erections. Is it possible that last night I had a near miss that produced a limited erection?