Error: 'TaskSetGapFinder FindGaps No Tasks in TaskSet' when added works order to the plan

Full error message when adding works order to the plan:
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​Add To Plan
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Order Code: 123456
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TaskSetGapFinder.FindGaps-No Tasks in TaskSet

Delete works order and create new one with relevant associated task and then import this works order into Orchestrate. The new works order will add to the plan fine.