Can an epigastric hernia be caused by an oesophageal reflux operation 5 years ago

Yes: Whether performed via laparoscopic or "open" surgery, i assume that you have a scar in the epigastric region. Hernias associated with midline incisions (incisional hernias) are not uncommon; all else being equal, elective repair with mesh is the standard rx, either thru a laparoscopic or open approach. I recommend that you contact a hernia surgeon. Good luck!

Yes: Especially if the lump is in close proximity to one of the small incisions. See your surgeon to check it out.