Been having this same problem myself, so frustrating. Its a V-Glide 97k and is absolutely stunning to shoot.
Zero the day before a comp, stacking pellets behind the crosshair only to find come comp day POI is anywhere between 0.5 - 1.5 inches high.
Reading through this thread the common trend seems to be V-Mach in its various guises. This is leading me to think the piston seal may be more/less efficient in different temps. I have another 97k with a standard piston seal and this does not experience POI change. I intend to try a standard seal on the V-Glide to see if this helps any.