I have noticed huge differences in readings between Sensei and iStat.
For RAM usage:
As you can notice iStat stays NordVPN is using 1 GB, while sensei shows 215 MB.
iStat says 1.39 GB for Xcode, but Sensei shows no value for it.
Safari is the same, iStat shows 3.93 GB, while Sensei shows 333 MB.
iStat shows 1.2% for Xcode, and Sensei shows 9.6% for Xcode and so on you can see how the values are different and some of them are completely missing from one of them.