Ethan Cutkosky broke his leg so it was written into the show.
Fiona's job at the Golden House Restaurant, organized by her parole officer last season, has magically relocated to Patsy's Pies. This is due to Jeffrey Dean Morgan's inability to reprise his role as Charlie Peters, the restaurant manager in recovery. The role was not just recast but renamed and relocated for Dermot Mulroney to play Sean Pierce. It could be argued that it is the same diner and that Peters resigned and the diner was renamed between the Season 4 finale and the Season 5 opener.