Potential eviction when Azure reclaims the VM is the correct answer.

Azure Spot virtual machines are offered at a discount because the provider can reclaim capacity when it is needed for higher priority workloads. That means your nightly batch jobs can be interrupted when capacity is reclaimed and you must design for interruptions with retries, checkpoints, or fallback to regular VMs.

They may sometimes cost more than a standard VM is incorrect because Spot VMs are typically priced lower than standard pay as you go instances and the trade off is availability not higher cost.

There is no uptime SLA for Spot VMs is incorrect in the context of this question because the primary operational risk being tested is the possibility of eviction and interruption. SLA differences may exist but the immediate effect on batch jobs is that instances can be reclaimed.

Quota limits on how many spot VMs you can run in a region is incorrect because quota limits apply to resources in general and are not the defining risk of using Spot VMs. The main issue for Spot VMs is that available capacity can change and cause evictions.

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