Channel has no point Connection

I just got a weird error when trying to build my OpenCL code with aocl:

Error Channel has no point connection: ID= in_channel_a
  avm_channel_id_in_channel_a_write connection misin, or optimized away

# pragma OPENCL EXTENSION cl_altera_channels : enable 
channel uint2 in_channel_a __attribute__((depth(1)));
channel uint2 in_channel_b __attribute__((depth(1)));
channel uint2 out_channel __attribute__((depth(1)));
__kernel void in_streamer_a(__global const uint2* in, uint n) {
    for(uint i = 0; i < n; ++i) {
        write_channel_altera(in_channel_a, in);
    }
}
__kernel void in_streamer_b(__global const uint2* in, uint n) {
    for(uint i = 0; i < n; ++i) {
        write_channel_altera(in_channel_b, in);
    }
}
__kernel void out_streamer_a(__global uint2* restrict out, uint n) {
    for(uint i = 0; i < n; ++i) {
        out = read_channel_altera(out_channel);
    }
}
__kernel void simplified_worker_kernel(uint n_steps) {
    for(int i = -1; i < n_steps; ++i) {
        uint2 write_data;
        uint2 current_a;
        uint2 current_b;
        current_a = read_channel_altera(in_channel_a);
        current_b = read_channel_altera(in_channel_b);
        write_data = current_a + current_b;
        write_channel_altera(out_channel, write_data);
    }
}