Sometimes when data has been archived and then restored, and it is to be re-archived you might encounter an issue where the items won't re-archive. Let's see why that might be:
When Enterprise Vault restore an item, it marks some additional MAPI attributes on each item:
When archiving happens again, these items won't be eligible because they are marked with these attributes. The attributes can be ignored, and there are actually three choices:
HKLM\Software\KVS\Enterprise Vault\Agents
[DWORD] IgnoreEVDates
0 = Off
1 = Ignore Archived date
2 = Ignore Restored date
3 = Ignore both Archived and Restored date
More information in this Connect Forum post: https://www-secure.symantec.com/connect/forums/restored-mail-not-archive-after-re-enable-mailbox#comment-1437041