The regexp which parses the LV timestamp's UTC offset formatted as string (%<%z>T) expects a leading "+" or "-" character, but "+" is omitted by LV for positive time offsets when converting it to string, so the regexp fails and returns an empty UTC offset string. You have to either adjust the regexp command to interpret a missing first +/- character as "+" (i.e. if the first character is a digit), or explicitly check whether the first character is a digit and prepend a "+" to the string before the regexp.
The regexp which parses the LV timestamp's UTC offset formatted as string (%<%z>T) expects a leading "+" or "-" character, but "+" is omitted by LV for positive time offsets when converting it to string, so the regexp fails and returns an empty UTC offset string. You have to either adjust the regexp command to interpret a missing first +/- character as "+" (i.e. if the first character is a digit), or explicitly check whether the first character is a digit and prepend a "+" to the string before the regexp.