We looked into this and it is dropping appropriately.
Alas, the issue here seems to be that over the last 15 days, you chopped down 360 Ironwood trees. In that time, your luck - which, as you mentioned, fluxuated a little bit due to removing and putting on luck gear, etc - wasn’t high enough to guarantee a drop of Ironwood Sap. That being said, if your luck had been consistent, you would have been guaranteed one drop. (90% of the time, though, you were well below your highest luck over the last 15 days.)
My suggestion would be to make sure your luck is higher when specifically looking for Ironwood Sap because it does directly impact your chances of it dropping.
I hope that helps.