Yeah, but you don’t jump from 30.86 straight to 29.92 in a second and the aircraft giving you warning. Then flips back to 30.86 within a few nm.
I would expect changes in barometric pressure like this to be within 1 hPa at any given time on approach. You know, like 1013, then 1014, then 1013 again. Or in inHg unit to be 30.86, then 30.85, then 30.86 again.
Sure, if you depart on one place at 30.17 and your destinatiuon at 29.86 is very common. But you would only change this barometric pressure once. And any discrepancies at one place is generally very small amount.