Shot pulling way too fast even at finest grind setting [Varia VS4]

Hey, so I've been using a Varia VS4 and had my previous beans dialed in at around 3.9. Great extraction, working as expected.

I switched to a new bag (medium-dark, roasted about 4 weeks ago) and had to grind much finer. The strange thing is that even at setting 1 (which is the finest Varia recommends) the shot doesn't really slow down. In fact, it seems to run even faster.

I'm dosing 18g in an 18g basket and getting about 70-80g out in 30 seconds. There's a huge amount of crema and the shot tastes too bitter for me.

I would have expected it to choke or at least slow way down at setting 1, but no luck.

Could this be a calibration issue or are these beans just way more soluble / lower density than my last bag? I was also wondering about staleness. They're 4 weeks post-roast, so not super fresh, but the crema is still massive. That's what confuses me.

I am quite clueless about what to do. Do you have any ideas?