There's currently a bug with chickens dying instantly to lava. In previous version (before 1.14 pre-release 1) chickens would be set on fire with a quick pulse lava dispenser, instead now they instantly die and their drops are burned.  The bug began in 1.14 pre-release 1 and was not mentioned in the patch notes as a change of feature, therefore I'm making the assumption of it being a bug. Below I've attached 2 videos, 1 in the last snapshot ( 19w14b) before 1.14, and 1 in current 1.14.4

Thanks.