When opening around a dozen vendor bags the lag goes red and stays that way for a while, then turns orange and eventually back to green. Observed lag time was around 800ms
Indeed, so don’t open them all in one spot, or in town.
When you complete a GR, go back to town, buy vendor caches, go back into the GR and open the caches one at a time, moving far enough away that each pile of loot is separate (so it’s easier to pick out red beams if you get one), repeat this until you’ve got a long string of shiny green / orange beams left behind you, port back to town, then close the GR.