Writeable inputs to FPGA I/O nodes can be left disconnected without any warning (or broken VI indication) from the VI in which the I/O node is used. This can cause some vigorous head-scratching if the missing connection is not immediately obvious as in the screen shot below. For obvious reasons, FPGA controls have no connector assignment or "Recommended, Required, Optional" attribute. In that case, and to avoid playing "Where's Waldo" on the block diagram, I suggest making FPGA I/O node input connections implictly "required", and if not, the VI would be broken. This would be the same behaviour as seen with cluster nodes.