I teach with Arduino and I see a couple hundred boards in a year. I had purchased a batch from a local supplier that were darker blue then the regular Arduino boards and that have a red power LED. Since this purchase i have had some students by the same boards off of Amazon. The boards all say made in Italy but are not official arduino boards, they resemble a lot of the made in china knock off stuff . Any way every single one of them has giving me the "Not in sync" error at some point in their lives. I can change the 328 but eventually, "Not in sync" re appears. Most these boards have hit the trash in my class room because they got to frustrating to trouble shoot with students.
Check the board for a red LED, it could be a knock off board sold to you as the real thing.