With perl:
perl -pe 's{^g(?:\d+/)*?(\d+)\K(?:/\1)+(?!\d)}{}' < your-file
It is strict in that it will remove the first sequence of repeating numbers only in the leading g/number/number[/number...]/number part and only if that part is not followed by a digit.
With sed, you could do the same with:
sed '
\|^\(g\([[:digit:]]\{1,\}/\)*[[:digit:]]\{1,\}\).*| {
h; # save a copy of original line
s||\1:|; # remove all but the leading g/x/y/z
s|\([g/]\)\([[:digit:]]\{1,\}\)\(/\2\)\{1,\}\([^[:digit:]]\)|\1\2\4|
G; # append saved copy
s|:\ng\([[:digit:]]\{1,\}/\)*[[:digit:]]\{1,\}||; # remove excess
}' < your-file