I was planning to make this video, but @Astro_Alneyadi does it better. For the nerds - in the usual linearized stability analysis for rotation about the intermediate principal axis I2, you’ll see terms involving (I3-I2)(I2-I1). When I3 almost equals I2, as is the case here, the (I3-I2) term becomes small, and the instability grows much slower than usual, leading to this dramatic flipping behavior.