I just came across this issue myself, and think I have the solution. For some reason the custom MetaHuman I added to my project did not have any of the Groom Bindings in place, so in animation, the hair, eyebrows, etc. did not move along with the head.
Opening the MetaHuman’s Blueprint, and selecting each of the hair groom components, I could see that the Groom Binding selection in Details under Groom was blank. From the dropdown next to this empty box I selected the corresponding Groom Binding for each hair component (Hair, Eyebrows, Eyelashes, etc.). For instance, my Hair groom asset was Hair_M_BobCurly, so the corresponding binding was Hair_M_BobCurly_f_head_Archetype_Binding
Once compiled, the hair moved with the head along with the animation appropriately. Hope it helps.