Looking at the photos of the two groups, and the way they merge together I'd say that that was the parachute seal altering the exit timing as temperature changes.
The temperature could change due to external conditions, or due to frequency of shots.
A good test is to shoot with two mins between each shot, so simulate a competition. If it doesnt shift then the rifle should be ok in a comp, so long as the external temp isnt very different from when it was zero'd, and if the temp doesnt change much in the day.
You should see that if you just blat out shot after shot the poi will shift.
One of my 97's has an O ring piston and doesnt do this. My vglide setup (sat in a drawer) did.
My diy 25mm tune hasnt done it...yet! Target tune india seal lubed with dry graphite.
I need to test if dry graphite lube will stop the vglide setup changing poi. After hols perhaps.