AuCTeX does not work if file name has numbers?

I created a simple Hello World file with the name plan_6000.tex. The file compiles perfectly using terminal commands. However, AuCTeX throws an error saying Undefined control sequence at line 1. Moreover, other commands like inserting environments, yasnippets, etc., are not working either. If I rename the file by removing the numbers, everything works fine. Is this a bug in AuCTeX?

I have Emacs 26.3 and AuCTeX 12.2.4. I am compiling using the xetex engine.

MWE:

documentclass{article}

begin{document}

Hello World.

end{document}

%>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
documentclass{article}

begin{document}

Hello World.

end{document}
%<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

% Local Variables:
% TeX-PDF-from-DVI: nil
% eval: (TeX-PDF-mode 1)
% TeX-engine: xetex
% eval: (write-file "plan_6000.tex")
% End: