Upgrade-sla sets Due to (not set )

Hello I have done the upgrade procedure to move from 4.2.12 to 4.4 version.
Cleaned cache, started my webserver, enable SLA on all queues and then run
the etc/upgrade/upgrade-sla scritp. I have noticed that the Due of all
tickets is set to (‘not set’). How can I avoid this?

Status: rejected
SLA: Incident
Priority: Lower/Highest
Queue: RT_support

2016-04-07 14:24:25 The RT System itself - SLA changed from (no value) to
2016-04-07 14:24:25 The RT System itself - Due changed from 2013-09-06
13:20:50 to Not set

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