I imagine this is not a unique problem but I was unable to find a straightforward answer.
I am a US citizen looking to travel to Europe for a bit over 90 days, let's say 100, but around 30-40 of those would be outside of the Schengen zone (Croatia and maybe Ukraine).
I will be landing in Italy and flying back home out of Germany.
I am concerned that I may have to deal with a suspicious official when I land and my return flight is longer than 90 days in the future. Additionally, I am wondering if I will run into any issues entering the Schengen zone for the second time (from Croatia). Do I need to keep any documents that prove I was outside of the Schengen?
Visual example of my plans; USA -> Italy (40 days) -> Croatia (30 days) -> Germany (30 days) -> USA
Should I expect problems?