My guess is that this line may not survive pre-compilation:
hnswlib = pyimport("hnswlib")
Can you try to define an object and then initialize it inside __init__ function, like this:
const hnswlib = PyNULL()
function __init__()
copy!(hnswlib, pyimport("hnswlib"))
end
Ref: https://github.com/JuliaPy/PyCall.jl#using-pycall-from-julia-modules