Convert tex to html with a xltabular

Question

I am trying to convert from tex to html. For this I use htlatex with the following command.

htlatex.exe %FILENAME%.tex "xhtml,html5,mathml,charset=utf-8" " -cunihtf -utf8"

In my tex file I use an xltabular. I get the following error message.

! Missing number, treated as zero.
<to be read again>
                   \ar:cnt
l.382 \end{xltabular}

That is the code of the xltabular

\begin{xltabular}{\textwidth}{l}
Test1\\
Test2
\end{xltabular}

Can anyone tell me where the problem lies I have no idea where the problem is. I can convert it to PDF without any problem.

Thank you in advance.