Broken fonts in WPF

So I have this application that many people use and sometimes there are reports of labels being corrupted. First picture is broken font and second is how it is supposed to look. Issue persists even if language is changed. The fonts used is just basic Roboto and the bug is very rare. I can ask the guy who has a problem to experiment with the app a bit and/or give him custom builds to try, but so far I just gave him the version of fonts that supposed to go with the app to rule out potential mismatch.