What you were expecting to happen, and what actually happened:
I have enough Forge scrolls to upgrade Doomed Tanto by1 level, but the upgradable icon does not appear and neither does the weapon appear when I search for upgradable weapons.
How often does this happen? When did it begin happening?
This happens with doomed weapons where I have just enough forge scrolls for the next level, in my case level 2 for brown, green and purple.
Steps to make it happen again
I first noticed this issue some time ago. It persists.
It might be better if it just considered something “upgradeable” if it isn’t yet fully upgraded. Without regard to whether you have the resources in inventory to upgrade it. I say that particularly now that orbs are a thing and it doesn’t seem to equate those orbs with having the necessary resources.
In my case, also Doomed Baton, Doomed Cauldron, Doomed Magi, Doomed Poignard, Doomed Potions. All are +1 and I have 2 forge scrolls available for each color. For the other doomed weapon colors with +1, I have more scrolls available and they are recognized as upgradable. Forging more scrolls might resolve the problem but not the bug.