We have a project, let's call it Foo, available at FooBar.com, but we also had another similar (but less successful) project called Bar, available at Bar.com
So as you might have already noticed Bar has shorter hostname and somehow it's more suitable for this particular project type. At some point we decided to sacrifice Bar project in favor of Foo. So moved the content of FooBar.com to Bar.com +
- we created a permanent redirect (HTTP 301) FooBar.com => Bar.com
- on Search Console we requested a redirect for FooBar.com => Bar.com
- on Bar.com we left the same Google Analytics ID as we had on FooBar.com
- ... and so on
during the next few days we noticed a very strange thing on Google Analytics: the number of visitors was quite the same, but the bounce rate increased dramatically (from 2% to 60-70%) and page-per-session ration has decreased by 50% (from around 5 to 2.5 pages per session). There is no reason for such changes, because the content is the same, only the hostname has change.
P.S. We have also noticed lower incomes from advertising systems, so it's not just about Google Analytics