Why did changing buffers change my POI?

[xoon]

The consensus is that bullets have left the barrel before any change in buffer weight influences the gun.

well i agree it has left *the barrel* but OP said he was using a suppressor.
Suppressors keep the system under pressure until the bullet exits the end of it. The system (16in mid length gas) goes from ~6.5 inches post gas port to ~13.5 or ~15.5 if the suppressor is in the 9 inch configuration.
How could this affect accuracy or POI?
well i believe it is widely acknowledged that suppressors can affect group sizes (sometimes positively sometimes negatively)
i think this demonstrates that accuracy can be affected after the bullet has left the barrel
my conjecture is that whatever mechanism causes suppressors to affect accuracy in general may be causing this particular issue
if i had to flesh it out more with a bit more speculation, something to do with rapidly changing and/or inconsistent pressures behind or around the bullet due to the bolt opening before the bullet has left the suppressor