Code issues on same code differ

Goodmorning,
I am evaluating Resharper free evaluation 7.1.1 version on a Windows Forms application made up by nine different projects, grouped into a single solution. I use Microsoft Visual Studio 2010.
I see that if I run the "Inspect code issues in current project" every day, on the same code, the results differ: for example, if a day I find 9500 issues, the day after i Find 9520. This despite no change has been done to code !
Anybody could explain a possible reason for this apparently incorrect ReSharper behaviour ??

Thanks a lot !