It's one thing getting 0/7 Rares from a full clearance of Cerulean Hills like I did for the first ever time yesterday.
But 0/9 in Tangleroot the very next day = You've gone and nerfed the Rare Spawn Rates haven't you!?!
P.S. Both times this has happened I've been on a Major Slayer Pot and I've noticed overall a distressing correlation between being on a Slayer Pot and Rare Spawn Rates being lower than average as opposed to when not on a Pot!