Service Accounts typically get locked at the target devices that is the server or servers the account is attempting to scan. These targets usually has policy that an account is not allowed to be logged in after a particular number of unsuccessful attempts.
When you say your service account is getting locked out do you mean that it is not able to scan any device or is not able to scan certain devices if only certain then what I said in the paragraph 1 applies and you would need to talk to your server admin to get the id unlocked. Discovery logs would typically not show this apart from saying that the access to server is denied. This kind of information gets logged at the server level logs and not in the discovery logs.
If your service account is locked altogether and is not able to login to any device then you need to contact your active directory administrator to check about the problems with service account.
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