What does the number in the custom node error Material.ush(2153,1-34) mean?

ue version 4.27

[SM5] /Engine/Generated/Material.ush(2153,1-34):  error X3511: unable to unroll loop, loop does not appear to terminate in a timely manner (27 iterations) or unrolled loop is too large, use the [unroll(n)] attribute to force an exact higher number