The weekly reports option now are reporting as Days instead of Weeks. Additionally the Visitors summary is showing the summary for only the last day in the report.
This was introduced in 1.11.x and after searching other bugs I could not find a related item.
With additional research it appears that 1.11.1 is not respecting the Week period specified and always used the Day. When I adjust the API.php file to force the week period the report generates without a problem.
In e3096c0359dd6ab23680c7224a1e0144fae86f1b: Use correct period when manually generating reports.
It is actually by design, that you can generate the reports for whatever period is currently selected. Reverting
In 89d41940a87d449114f529df115b62d3987f88ce: Fixes #3884 #4014 in twig branch
In 2a28755ea66ef1355839bc2bee050db13b53648f: Fixes #3884 #4014