There's not a lot of information here to really offer any help. Did you verify that your ESM instance actually has the valid/updated license file so it actually has the correct license status? Did someone accidentally revoke the license to a bunch of active agents? Are ESM's services actually running?
IF the agent is not communicated with traps server within the revocation period, default value(90 Days) ,the ESM released the license from the particular endpoint and that will showed as unlicensed.You can change the license revocation period from} Setting}Agent Setting}license revocation period
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