I have finally a prototype in the lab. It appears there is indeed a catch with the VDD and VIN.
I have 24->12V buck SMPS supplying VDD and VIN left floating as recommended. The SMPS does not start as at least 12.7V voltage is required to start the device. For prototype I can adjust the VDD voltage to 13.8V without problems.
For similar functionality as in the "intended" setup I'd connect 24V to VIN and 12V to VDD. After VIN has exceeded 12.7V, VDD threshold drops to <9V.