You can find Sculk sensor in natural blocks and redstone

Seems to work as intended. Sculk sensors both generate naturally and give a redstone output, and items are allowed to be in two different categories at once as of this snapshot.

WAI

I'd say this is an issue. No other MC block that fits 2 categories are in 2 different Creative Mode menus. 

Logs are both in building blocks and natural blocks.

I can confirm this behavior though I'm heavily inclined to believe that this isn't an issue and is working as intended. Sculk sensors generate naturally in the deep dark biome, therefore making them fit into the "Natural Blocks" creative tab, and on top of this, they also give out redstone signals (are a redstone-related block) therefore making them fit into the "Redstone Blocks" creative tab as well.