Some End cities do not spawn with an End ship

No this is normal, not all end cities spawn with an End ship. End ships are the only End city structure that can have an elytra.

Not a bug

Thank you for your report!
However, this issue is Working as Intended.

The report you have submitted is working as intended: It's about 50% chance for End Ship..

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Things such as graphics, sounds, world creation, biomes, redstone, villagers, and animals may not work the same in current versions.

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