see below

Peut-être!

According to Termium. Hope this fits into your context.

Example:
Mixed performance under last year's program; obtained emergency assistance in November 1992, hoping for ESAF (Enhanced Structural Adjustment Facility) program in 1993. Le programme de l'an dernier a donné des résultats mitigés; aide d'urgence obtenue en novembre 1992, dans l'espoir qu'une facilité d'ajustement structurel élargie sera mise en place.

While "mixed" could be OK,and one often sees it in business/financial contexts, I think you would do better in this case to use the direct equivalent, "mitigated". It will give the reader the desired sense of mixed, non-definitive, perhaps non-optimal results.
It seems to me that you will be "safe" in choosing this translation as it is very commonly used in reporting on results of medical treatment and research in numerous fields, whether biology, the pharmaceutical industry, education, economic development, sociology, etc.
A few examples can be found in the sites listed under References and the one pasted below. Just use the "find" function in "Edit" to get to the relevant phrases quickly.

http://groucho.onr.com/hftp/BottomLine/backissues/1999/Feb-M...
see:
"Previous empirical studies ... have produced mitigated results."

Best regards, D. Guessous

This is business usual term.