Since you bought the computer in March, you're covered under Applecare. A phone call to Apple seems to be in order, especially because this issue appears to be related to Apple installers and/or Lion.

Jon

macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365