Hi there is a bug with the Esbern's Potion even when drinking it it does nothing
except state that you gain the perk dragon infusion but i don't end up getting
the buff that everyone says it does there is a little code you can
write into command to make it appear
player.addspell 000f5ffa
try not using this to cheat
the spell gives you an active effect 25% less physical damage from dragons.

Hm same problem here.
I think the quest's ID is 000E6DF1 - at least it advances to queststage 10 after getting the quest to fetch dragon bone and scale. And it advances to queststage 100 after getting the potion which does nothing.
showqueststages "000E6DF1" also only displays two possible stages (10/100) and manually advancing it via setstage "000E6DF1" 100 correctly removes dragon bone and scale - giving you the potion which does nothing - but the quest still remains.
Oh well at least we got the perk, thanks for that .