"Rich" skrev i melding
...
=MONTH(H6)
and have the format of the cell set to mm the value is
stuck at 01 and I cannot understand why.
=YEAR(H6) works fine.

It's not very obvious what you expect to see. MONTH returns the month
/number/. YEAR returns the year number -which usually is just fine. If you
want to see "feb" or "oct" then either
=TEXT(H6,"mmm")
for returning the real text, or
=H6
format cell as "mmm", for keeping the date and just display the text.
=MONTH(H6) formatted as mmm will always return jan btw, so son't do that.

HTH. Best wishes Harald