The siege date is in the sql. No idea why it happened like this to begin with, but if you fix the siege dates appropriately, after the siege takes place it should be properly rescheduled for some time a few weeks later. My guess is that it was messed up via an ingame gm command
To change the siege date, you can lookup the ingame gm commands for sieges while the server is running, or you can edit your database while the server is down. However, the latter step requires some additional knowledge about sql and unix-style date-time fields.
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