CTest produces its results in subdirectories named after the date and time. As the older ones are not automatically removed, xUnit is tricked into thinking that there are testresults that were not updated.

It is not a blocking problem since a user can always remove them in the job script.

But if you are unaware of this you will either get failing jobs (when "Fail the build if test results were not updated this run" is set) or an ever increasing number of test results (when it is not).