How to debug "Local instance of remote reference not found"?

I tried to make a self-contained MWE but can’t replicate the error.

For some reason it doesn’t like the @sync:

    @sync @distributed for d in 1:ndocs
        thetaLoop!(Theta,Achain,J,d,n_burn,Alpha,verbose,nchains,startiter,niter,k)
    end

thetaLoop! refers to:

function getAllTheta(Achain,J,Alpha,startiter,niter,nchains,k;verbose=false)
    n_burn = niter-startiter-1
    ndocs = size(J)[2]
    Theta = SharedArray(zeros(n_burn,k,nchains,ndocs))
    @sync @distributed for d in 1:ndocs
        thetaLoop!(Theta,Achain,J,d,n_burn,Alpha,verbose,nchains,startiter,niter,k)
    end
    Array(Theta)
end

function thetaLoop!(Theta,Achain,J,d,n_burn,Alpha,verbose,nchains,startiter,niter,k)
    for j in 1:nchains
        for i in 1:n_burn    
            verbose ? println(myid(),": doc $d, iter $i") : nothing
            nji = getZ(Achain[startiter:niter,:,:][i,:,j],k)*J
            Theta[i,:,j,d] .= vec((nji[:,d] .+ Alpha) ./ sum(nji[:,d] .+ Alpha))
        end
    end
end

Error:

ERROR: LoadError: TaskFailedException:
On worker 2:
Local instance of remote reference not found
channel_from_id at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Distributed/src/remotecall.jl:164
init_loc_flds at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/SharedArrays/src/SharedArrays.jl:426
deserialize at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/SharedArrays/src/SharedArrays.jl:483
handle_deserialize at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Serialization/src/Serialization.jl:842
deserialize at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Serialization/src/Serialization.jl:1350
handle_deserialize at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Serialization/src/Serialization.jl:837
deserialize at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Serialization/src/Serialization.jl:1350
handle_deserialize at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Serialization/src/Serialization.jl:837
deserialize at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Serialization/src/Serialization.jl:773 [inlined]
deserialize_msg at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Distributed/src/messages.jl:99
#invokelatest#1 at ./essentials.jl:710 [inlined]
invokelatest at ./essentials.jl:709 [inlined]
message_handler_loop at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Distributed/src/process_messages.jl:185
process_tcp_streams at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Distributed/src/process_messages.jl:142
#99 at ./task.jl:356