I came upon the same issue, except I am working only in 4.27.2 so your info about this working in 4.26 surprised me. At first I thought the Groom/HairStrands are just not supported under Linux/Vulkan, as there is just no information out there.
So, did you by any chance managed to make it work in 4.27?
Hey,
I am using Unreal 5.0.1 and this issue happens to me as well, but it only occurs when I build for Linux in shipping option, when building in development mode it works fine, anyone find a solution yet?