I had this today with Simeon, which was weird since his friendship bar is max green with my spellcaster. Then I started thinking and checked, and my spellcaster has learned all the spells that she can learn at her caster level. When she asks Simeon to teach her a new potion, he says she's learned all she can.
In my case it's clearly just a lack of appropriate refusal text, the sage uses the 'don't know you well enough', instead of explaining that you need to get to the next level before you can learn new spells. Not sure if this is the case with the others, but worth checking.
@Lumiasta That...makes so much more sense, thanks for mentioning it! I've also had this issue with Simeon despite the relationship panel saying I was "good friends" with him, and I bet it's because I've learned everything for my current caster rank, I hadn't even thought of that as an option. I've talked to him the most because I've been focusing on learning practical magic more often than the others, so that would explain why I'm still able to learn things from the other sages but not him at the moment.
It would be great if the text telling your Sim that they've learned all they can specifically mentions their caster rank when that's the limiting factor, because I was also a tad confused when getting the "you've learned all the potions" message when my spellbook clearly showed I hadn't yet.
