[cloche]

Yes I am struggling with this exact situation. A person on my team fits this profile. They can do the work. It's just that their output is below average except for the times when we've had serious discussions about their performance. They will improve for maybe a month or two before regressing back to their previous level.

[myrandomcomment]

Fire them. They are wasting your time. Their yo-yo output will be something that is noticed by the rest of the team which is demotivating for them. You gave them a chance.