Definition of resume:
resume |riˈzoōm|
verb [ trans. ]
begin to do or pursue (something) again after a pause or interruption : a day later normal service was resumed.
• [ intrans. ] begin to be done, pursued, or used again after a pause or interruption : hostilities had ceased and normal life had resumed.
• [ intrans. ] begin speaking again after a pause or interruption : he sipped at the glass of water on the lectern and then resumed | [with direct speech ] “As for Joe,” the major resumed, “I can't promise anything.”
• take, pick up, or put on again; return to the use of : the judge resumed his seat.
Now, According to that definition, when you "resume" something, it notes that you stopped doing something and continued.
I could see two things here, when you travel on AP. You are no longer in the US "waiting" on your process of adjustment of status. But, that does not mean that USCIS puts a hold on the process necessarily.
I mean, just because you are on vacation, it does not mean that USCIS is.
Meaning, if you are gone on AP, the process continues (IMHO). You will still get an RFE or your Interview Letter and Appointment. If you are gone on AP and do not come back before your interview. It will be deemed abandoned.
So when you do come back, you resume, to do your waiting... but USCIS is still and has been working (
slooooowly).
The only time your application is put on hold/pause is when they send you an RFE.
That is how I see it.