Not sure if this is a bug, or what but when you read the help file for Elven Arcanum it says Elf/Delf and invoker are the prereqs. However when I discuss the prereqs with the guildmaster I am told I will never be able to learn this.

Where is the disconnect in this?

'ELVEN ARCANUM'
Invokers of either elven or dark-elven heritage are able to
use their high intelligence to engage in more consistently skillful
spellcraft ability.

This edge requires your intelligence be high to have any results.

See also: EDGES

discuss guildmaster prereq elven arcanum
You will never be able to learn Elven Arcanum.