It seems that this issue is known, this is a code comment from common-info.tex:

% Eitan's commented-out definition started like this (and doesn't work):
%\def\CleanComment #1tex4ht-info#2#3#4.#5>#6//{[\eatIV#4% <--jobname
%
% Eitan's active definition started like this:
%\def\CleanComment #1tex4ht-info#2#3#4.#5>#6//{[#4% <--jobname
%
% However, that didn't work either. #4 is not the jobname.
% The arguments when running htlatex tex4ht-info-mml.tex are these:
% %#1<-
%\CleanComment #1tex4ht-info#2#3#4.#5>#6//->
%[\if ,\ifnum \FIRST =#6 .\else ,0\fi
%#1<-
%#2<--
%#3<-m
%#4<-ml
%#5<-html#QPrTx1"\<infomml\
%#6<-92\ifx \CodeId \:gobbleii \else ...\fi
%
% As a result, when running mzlatex hello.tex xhtml,info there was
% an error on the first line of infomml.4ht, which looked like this:
% \ifx\infoIVht\UnDeF\def\infoIVht#1//{}\fi\infoIVht[ml0]28...//
% That "ml" is not a number, so \ifnum fails. This only happens
% mzlatex and the info option, not htlatex. We don't understand.
%
% This version avoids the spurious "ml" but mzlatex hello.tex still
% fails, trying to process the \ConfigureHinput blocks as text.
% Changing the bracketed number in infomml.4ht to small values seems
% to make it pass, but can't see how to generate it. The number
% after the brackets (#6) changes also.
%
% Since all this is only about the info option with mzlatex,
% just leaving it failing for now. Other things to do.

tex4ht-info-mml.tex contains only few lines, it is a question whether it isn't better to incorporate the information into other info files, or remove it completely.

I also tried to fix the problem, but it is one of these really esoteric areas, and I wasn't successful.