I'd change your preamble to:
\usepackage[ngerman]{babel} \addto\captionsngerman{ \renewcommand{\figurename}{Abb.} \renewcommand{\tablename}{Tab.} } \renewcommand{\thefigure}{\arabic{section}.\arabic{figure}} \@addtoreset{figure}{chapter}
I'd change your preamble to:
\usepackage[ngerman]{babel} \addto\captionsngerman{ \renewcommand{\figurename}{Abb.} \renewcommand{\tablename}{Tab.} } \renewcommand{\thefigure}{\arabic{section}.\arabic{figure}} \@addtoreset{figure}{chapter}