As you can see in the image below the cursor is over power supply blocks and the yellow box isn't visible. I am in build mode.
I've noticed this issue several times. It happens when I put down a long line of blocks. In this case I put down 100.
The initial disappearance happened around block 70 or so. I figured that out by putting lights down up to where I could. However doing so made the position change to closer to 90.
At that point I jumped out of ship and went back their to see if they could be ran into. They can. Getting back into the ship the problem still persisted not being able to place blocks on them.
It appears there are two sections of your program that have to know about the blocks and the one that handles your cursor looking at them isn't seeing it. the blocks are obviously being displayed and boundaries for objects running into them exist. Just unable to target them with the cursor. That or you have a build property that prevents them from being targeted with the cursor. Any just a guess on my part I have no idea how your code is setup.
{F3390}