You might have meant to use a word other than "sporadic." That word describes a recurring event that happens at unpredictable intervals, such as snow in a norma

You might have meant to use a word other than "sporadic." That word describes a recurring event that happens at unpredictable intervals, such as snow in a normally hot desert, or a Linux crash caused by a race condition. Other words that fit the sentence better are "unusual," "unexpected," "unjustified," "inappropriate," "surprising," "extreme," "abrupt," or "out of the blue." (For what it's worth, I'm American, and I disagree with your assessment. We don't know how long the person was given to make progress, and we don't know what was communicated. To conclude that a two-week period without a commit represents the entire period between the start of the poor performance and the termination is, well, a bit out of the blue.)