Solved

5 stars staff

It's a known thing that sometimes staff one level above the manager level becomes available. I don't know how the game exactly applies the star rating but levels seem not to be fixed numbers and thus likely subject to rounding, thus rounding errors and errors that might come from some parts of the game comparing those levels as their real value and others use the rounded. I suspect that both those issues that higher level 5 yellow star staff becoming available and that sometimes some same level staff get shown 4.5 stars and others 5 stars are both part of some rounding error.

So if you see that kind of staff and they fit into your team then hire them, they shouldn't needing replacing next level up, at least with some luck.