Hey All!

For some reason I am unable to use Lando's butcher knife. Tried "R"  "F5" even clicking on the ikon in the circle. 

Also tried changing channels, discarding and re accepting the knife, no succes.

Any advice appreciated!!!

You need to use CTRL+ scroll wheel to swap to the "butchering" action as default, while hovering over the wheel above the chars head. Otherwise you cannot gather with the knife

Aye, also right next to "Butchering" there's (F5). You can press F5, does the same thing, for me at least. If you play on laptop you might want to switch the functions.

And maybe fix the interface so that it starts out with the equipped tool selected?  That whole selection interface should only appear with the toolbag equipped in the first place. 

You should be using a toolbag which contains all of your tools. It remembers the last tool you used as far as I can tell.

I was recently revisiting this quest to get the lamb meat for the hawks.  Tons of lamb meat no completion for the quest.  For the life of me, I could not figure out what I was doing wrong not to complete the quest.  As it turns out, I was using my personal butcher knife (from the tool bag) and not Lando's knife.  If you are having issues using Lando's equipment, use your own but remember you must at some point equip his knife to get the quest complete.  Same goes for the matchlock, axe, etc..

Have fun!

F on the chat, what to do if you deleted the butcher knife before you equipped it ?

If you deleted it and still have the quest, simply talk to Lando to re-obtain the item. 
https://bdocodex.com/gl/item/66174/