Floatrow package conflicting with centering longtable

Question

Consider the MWE below. If I \usepackage{floatrow} the longtable is not horizontal centered. If I comment out \usepackage{floatrow} the table is properly horizontal centered.

How can I get this snippet working (both use floatrow and center the longtable)?

Credits: Landscape construction (stripped down by me for MWE): Steven B. Segletes in this answer.

Without usepackage floatrow in below MWE (correct):

With usepackage floatrow in below MWE (not centered anymore):

MWE:

\documentclass{article}
\usepackage{booktabs}
\usepackage{longtable}
\usepackage{pdflscape}
\usepackage{afterpage}
\usepackage{setspace}
\usepackage[a4paper]{geometry}
% >> 'PROBLEM' package
\usepackage{floatrow}
% << 'PROBLEM' package
\begin{document}
Document is portrait
\afterpage{%
    \clearpage% Flush earlier floats (otherwise order might not be correct)
        \newgeometry{left=1cm, right=1cm,top=1cm,bottom=1cm}
    \begin{landscape}% Landscape page
        \pagestyle{empty}
        \centering % Center table
        \vspace{0pt}
        \begin{singlespacing}
\begin{longtable}{rr}
 \caption{Table is landscape.}
 \tabularnewline
 \textbf{Col1} & \textbf{Col2}\tabularnewline
 \midrule
 \endfirsthead
 \caption{Caption (Continued)}\tabularnewline
 \textbf{Col1} & \textbf{Col2}\tabularnewline
\midrule
 \endhead
 \bottomrule
 \multicolumn{2}{r}{Cont}
 \endfoot
 \bottomrule
 \endlastfoot
 A & B \tabularnewline
 C & D \tabularnewline
\end{longtable}
    \end{singlespacing}
    \end{landscape}
    \clearpage% Flush page
}
\restoregeometry
\end{document}

Answer 1

For some strange reason floatrow sets \LTleft and \LTright to 0pt breaking longtable's default positioning, you could set them back, or simpler just use

\begin{longtable}[c]{rr}

to force longtable to centre.

---

this is sort of mentioned in the floatrow manual

Alignment Settings for longtable. The floatrow expands some settings of table lay- out to the longtable environment, so you may set \LTleft and \LTright parameters inside \DeclareMarginSet settings. For example, centering option was defined like: \DeclareMarginSet{centering}{\setfloatmargins{\hfill}{\hfill}% \LTleft=\fill \LTright=\fill}