I have been using Arduino boards for years and never received the not in sync error. For people having the issue: something is happening to the 328 itself or the bootloader is getting damaged, which leads to the problem.
That "something" can be a huge list of things. It could be something so minor that you don't even remember doing it. E.g. changing connections while the board was powered. (Yes, I'm sure you'll argue you've never done that. Everyone says that, but everyone does it at least once.) My point is, seemingly minor actions could have caused damage. Damaged components don't fail immediately.