First, you have a syntax error in the
\patchcmd line, because you're missing a brace pair:
This has no consequences in this case, because the patch fails, so
\begin that was absorbed as the fifth argument is delivered because of the failure.
Main reason: the
\chapter macro has no
\clearpage in its replacement text, which is
and it is
\scr@startchapter that must be patched
% scrbook.cls, line 4030:
\expandafter\SecDef\csname @#1\expandafter\endcsname\csname @s#1\endcsname
Always check the meaning of a macro, before trying to patch it.
You probably want to remove both
I find it convenient to add something like
\ddt, which will warn about failure with
Undefined control sequence \ddt. When I'm sure the patch succeeds, I remove it.