The sleepstudy problem is a bug for the German language adaption of powercfg. With me it typically works, when I give a longer duration.
powercfg /sleepstudy /duration 20
Later it often works with the default duration as well. The bug can easily be seen in the xml output of sleepstudy
powercfg /sleepstudy /xml
This output is obviously used in an intermediate step in creating the html-output as well. In German language, the xml is not correct:
[...]
<Warnings>
<Warning Header="Hinweis: Dieser Bericht enthält keine Informationen zur ersten Sitzung vom Typ "Verbundener Standbymodus"." Body="Die erste Sitzung vom Typ "Verbundener Standbymodus" wurde in einem früheren Zeitraum gestartet. Wenn Sie sich für den früheren Zeitraum interessieren, verwenden Sie "<code>powercfg sleepstudy -duration DURATION</code>". Beispiel für die letzten zehn Tage:<br /><pre>powercfg sleepstudy -duration 10</pre>"></Warning>
</Warnings>
[...]
Qoutes don't nest like parentheses ...
BTW. powercfg /batteryreport also has problems in German language, it does get confused by German "," as a decimal seperator vs. Englisch "." and shows mW instead of W. Not sure, whether this is the reason for sometimes strange calculations of batteryreport. (I had written a program to transfer the xml output to Excel and then all calculations are reasonable).