Why the latency happens for recorded audio from a digital source

[Rockman413]

Hi there,
Maybe this more related to audio basics, and maybe this doesn't matter as we probably can't hear any difference, but I just want know some basics regarding digital audio how it works.

So I have 2 DAW running, I sync PT and DP via MTC. I play a drum hit sound in DP and have it output via loopback (or ADAT, etc..) and record into PT. Every time the exact position of such hit sound is slightly different.
I can understand there'll be a lantecy for me to hear this sound in PT, as there's roundtrip latency and because it's live record there's no delay compensation. But why the recorded position is also different every time? There's a one trip latency in this "roundtrip latency" ? Shouldn't PT automatically compensate for this delay and put the recorded audio at the correct position every time ?