February 2021
All I got out of that was:
"This time, the heirloom event will reset the number of spiders previously opened. I have opened 500 spiders before and after my account, but still no heirlooms. Do you have this situation?"
All I can say is that the game obviously doesn't like everyone having at least one heirloom. Someone bought 501 packs way before the event, and still haven't gotten theirs.
February 2021