What kind of record does contribution percent come from? It's on the sales team tab of the entry form for opportunities. Trying to locate a relevant script or workflow using StrongPoint and it's not on the opportunity record.

@reptar The Sales Team, including Contribution Percentage, defaults from the Customer's Sales Team tab, but the values can be entered or modified directly on the Opportunity

Is it possibly scripting on the form itself? What is the behavior you are trying to figure out?

Employee had the wrong role. It was preventing him from editing Contribution %. Problem solved.