Hey teamdevosjes, thanks for the bug report! I just tested this and it turns out that mobs actually can spawn in sugar cane.
![A Minecraft screenshot showing a floating platform made of grass blocks with sugar cane on top and waterlogged stairs to hydrate the sugar cane. Two zombies have spawned on two of the sugar cane-covered grass blocks. Nothing has spawned on the stairs and none of the grass blocks are left uncovered. A Minecraft screenshot showing a floating platform made of grass blocks with sugar cane on top and waterlogged stairs to hydrate the sugar cane. Two zombies have spawned on two of the sugar cane-covered grass blocks. Nothing has spawned on the stairs and none of the grass blocks are left uncovered.](https://i.imgur.com/oqoADxV.jpeg)
But aside from that, I did find some issues with how MobSpawnESP was checking for spawnable blocks, and those will be fixed in the next update.