I have LastPass Premium and use the Mac desktop app, Safari extension, and iOS app.
On the Mac app, the "Security Dashboard" shows me a security score of 92.1%.
On the iOS app, the "Security Challenge" gives me a score of 91.1%. The iOS app doesn't appear to provide a way to exclude a pwd from the security score. Perhaps this is the difference?
I would expect these two features to really be unified, though I understand the UI needs to differ to accommodate the mobile experience. I find the mobile feature provides more details, but the desktop app is easier to operate, to see the list of passwords that are reused, weak, or excluded easily.