I started up a new creative world to try out some designs, placed a fence down, and noticed that if I placed a fence on top of it, the second fence was invisible. I played around with it and found that it only happens in some areas, as seen by the screenshot. This one is going to be hard to repro I'm sure. I didn't use a seed.
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That you didn't use a seed doesn't mean that the Minecraft world has no seed, it just randomly generates one. Please use /seed to get the seed and tell us.
The seed is 2409925020304925578.
While messing around I noticed the bug happening sporadically with all types of bricks. There would just be patches where I could not place a fence, or stairs, or glass, and have it be visible. Exiting the world and re-entering it causes the objects to be visible again, but I would run into a different patch later on.
Upon leaving the world and rejoining it, the fence reappeared and it doesn't seem to be happening anymore.