A system that is more than a few years old may be having an underlying problem with its hard drive. When you rebuilt the O/S you may have only done a quick format of the hard drive which wouldn't catch serious problems with the drive. A great program to test the hard drive is SprinRite by Steve Gibson over at http://www.grc.com. When I get a new drive I run SpinRite and try to run it once or twice a year on my drives to help solve these type of problems.
The most beautiful phone ever has one wildly annoying issue
The Samsung Galaxy S8's fast speeds and fantastic curved screen make it a top phone for 2017, but the annoying fingerprint reader could sour your experience.