I observe crazy surge in joinmarket activity (I am running a join maker). Nothing for the past two weeks, and around 4 coinjoins just today. And they are paying crazy transaction fees, like 300 sats/vb.

This must be related to Samourai crackdown. Natural explanation is just people who would use Samourai. But I wonder if it is some sort of sting operation. Although not sure if the latter makes sense.