There is a Bug, when you cure a zombie Villager, the Villager is automatic switch his profession to any profession. There's no job site block around the Villager but it still switches by it own.
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Cleaning up old tickets: This ticket had been set to 'Awaiting Response', but has not received a response from the reporter (~3 months+) so is being closed as Cannot Reproduce. If you feel this is still a valid issue then please comment, or create a new ticket following the Issue Guidelines which includes steps to reproduce the problem.
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Is this still an issue for you? Note that villagers will search quite a long way for the nearest job block and it does not currently have to be visible to the villager or player for it to be linked.