@z3ntu, @Ingo : Yes, a hint would be a good Idea. I saw this recently on my Samsung Galaxy SII (running LineageOS 14.1)
@Roboe: The " Can’t install this package on top of incompatible data. Please try another package or run a factory reset. Updater process ended with ERROR: 7" problem. See Can’t Flash LineageOS
You can work around this by removing OS checks in the updater-script. Which is generally a Bad-Idea™.