What causes OpenCL to insert arbitration for local memory accesses?

I know FPGA OpenCL is deprecated in favor of OneAPI, but I hope you can help me anyway. I've created a MWE of a kernel for which the compiler inserts arbitration:

__attribute__((uses_global_work_offset(0)))
__attribute__((max_global_work_dim(0)))
__kernel void
kmain(uint n_tics,
     __global const volatile uint * restrict dsts) {

    float frontier[100];
    #pragma disable_loop_pipelining
    for (uint i = 0; i < 100; i++) {
        frontier[i] = 0;
    }
    uint nqueue[100];
    uint nqueue_n = 20;
    for (uint t = 0; t < n_tics; t++) {
        for (uint i = 0; i < 100; i++) {
            float tmp = frontier[i];
            frontier[i] = 0;
        }

        for (uint j = 0; j < nqueue_n; j++) {
            uint src=nqueue[j];
            frontier[dsts[src]] += 50;
        }
    }
}

So first I reset all elements of frontier. Then the simulation loop starts and I read one element from frontier and clear it. Then I add 50 to the values at the indexes given by another variable. I know the kernel reads from uninitialized memory, but it's beside the point (I think). In the report aoc complains about "Potentially inefficient configuration" and I can see that it has inserted arbitration circuits (see screenshot).

So the question is why? And how can I fix this memory access pattern to be arbitration-free?