You can't use `\unskip' in vertical mode

Question

So I have this strange error You can't use `\unskip' in vertical mode in springer latex template. For whatever reason, this is caused by the blank line before the last \end{proof}. Not sure how to generate a smaller example either.

https://www.overleaf.com/2166494628jhkmqjhhjjsv

\documentclass[sn-mathphys,lineno]{sn-jnl}% Math and Physical Sciences Reference Style

\usepackage{microtype}
%\usepackage{xfrac}
%\usepackage{mathtools}
\usepackage{enumerate}
\usepackage{bbm}
%\usepackage{mathbbm}
%\usepackage{thm-restate}
\usepackage{subcaption}
\usepackage{cleveref}
\usepackage{comment}
\usepackage{xcolor}
%\usepackage[textwidth=20mm]{todonotes}


\jyear{2022}%

%% as per the requirement new theorem styles can be included as shown below
\theoremstyle{thmstyleone}%
\newtheorem{theorem}{Theorem}%  meant for continuous numbers
%%\newtheorem{theorem}{Theorem}[section]% meant for sectionwise numbers
%% optional argument [theorem] produces theorem numbering sequence instead of independent numbers for Proposition
\newtheorem{proposition}{Proposition}% 
%%\newtheorem{proposition}{Proposition}% to get separate numbers for theorem and proposition etc.

\newtheorem{example}{Example}%
\newtheorem{remark}{Remark}%
\newtheorem{lemma}{Lemma}
\newtheorem{corollary}{Corollary}

\theoremstyle{thmstyletwo}%



\theoremstyle{thmstylethree}%
\newtheorem{definition}{Definition}%
\newtheorem{claim}{Claim}
\newtheorem{inva}[theorem]{Invariant}

\raggedbottom
%%\unnumbered% uncomment this for unnumbered level heads
%%end of Springer Template 

\newcommand{\hcom}[1]{\textcolor{blue}{#1}}
%  \newcommand{\mmcom}[1]{\mytodo{agcolor}{#1}}

\newcommand{\mmcom}[1]{\textcolor{red}{#1}}

\newcommand{\algorithmautorefname}{Algorithm}
%\newcommand{\definitionautorefname}{Definition}
\newcommand{\trw}{\operatorname{tw}}
\newcommand{\pck}{\operatorname{pack}}
\newcommand{\cover}{\operatorname{cover}}
\newcommand{\lemmaautorefname}{Lemma}
\newcommand{\corollaryautorefname}{Corollary}
%\newcommand{\claimautorefname}{Claim}
\newcommand{\propositionautorefname}{Proposition}
\newcommand{\sectionautoref}{Section}
\newcommand{\remarkautorefname}{Remark}

\newcommand{\poly}[1]{\operatorname{poly}(#1)}
\renewcommand{|}{\vert}   

\begin{document}

Let us give the details of the claim in   \cite{ErdosPosaFlorent} that even cycles satisfy the Erdos Posa property with bounding function $f(k)=131k$.

Let $\mathcal{D}$ denote the class of diamonds, that is, graphs that are a subdivision of the graph on two vertices with three parallel edges between them. 
Given a set $\mathcal{H}$ of graphs denote by $ \pck_\mathcal{H}(G)$ the maximum number of vertex disjoint copies of graphs in $\mathcal{H}$ and by $\cover_\mathcal{H}(G)$ the minimum size of an $\mathcal{H}$-transversal, a set of vertices $X$ for which $G \backslash X$ contains no subgraph isomorphic to a graph in $\mathcal{H}$.
Let $\trw(G)$ denote the treewidth of $G$.
For  $x \in \mathbb{R}$, denote by $\lceil x \rceil $ smallest integer larger than $x$.

%%Denote by $\mathcal{D}$ the set of diamonds


That even cycles satisfy  Erdos-Posa with $f(k)= 131k$ follows as a simple consequence of the following result of  Fomin, Saurabh and Thilikos  \cite{FominErdos}.

\begin{theorem}\label{packing diamonds}
\cite{FominErdos}  For a planar graph $G$ $\pck_\mathcal{D}(G)  \leq   131 \cover_\mathcal{D} (G) $.
\end{theorem}


\begin{lemma}
For a planar graph $ G $, $\trw(G)  \leq 37 \pck(G)^{\frac{1}{2}}$.
\end{lemma}
\begin{proof}
% We show  $\trw(G)  \leq 18 \lceil  \pck_\mathcal{D} (G)^{\frac{1}{2}}  \rceil +1 $.
%%  We need the following result of   Robertson, Seymour and  Thomas.
The following lemma  
 \begin{lemma}\cite{SeymourGrid} 
 Let $g \geq 1$ be an integer. 
 Every planar graph with no $g \times g$ grid minor has tree-width   $ \leq 6g-5 $
 \end{lemma}

\end{proof}



\bibliography{temp, EvenCycleTransversal} 

\clearpage
\pagebreak
\appendix


\end{document}