Strongholds do not seem to generate on the worldtype "Caves" nor "Floating Islands."
I've created multiple caves and floating islands worlds with different biomes:
Dark Forest Hills
Wooded Hills
Mountains
When using /locate stronghold on these worlds nothing came up. The method does seemingly work on normal single biome worlds with each of these same biomes selected.
Environment
OS: Windows 7, Java version: 1.8.0_201 (64bit)
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