For reference I found the Windows app to be a bit inconsistent, I would use either the website, or the command line version of the software as it provided the most consistent results.
FWIW I've also seen a few inconsistencies as well, including once where the app refused to show download speeds higher than 100Mbps on my laptop when. I could use a browser or iPerf and get great speeds, but the app just seemed to be stuck. About a week later it magically fixed itself.
With the new testing methodology they're using which does include data from multiple speedtest.net servers it will be interesting to see how it affects results.