So, I've been having this bug where in every playthrough there will be a certain class of trainer that won't train me. I seem to recall the most recent one being destruction. I can go up to the NPC and ask for training, they'll respond with their standard line along the lines of "I'll teach you, but I won't be held responsible for what you do with the knowledge" and then the dialogue ends and the training window never opens.
This question is distinct from this one by the fact that the dialogue option is there and they act like they'll train me but never do. I've also used mod added trainers that are supposed to be able to train you no matter who you are.
I also would like to mention that while I have mods that remove the 5 times per level limit and allow master trainers to train up to 100 in the skill, this issue occurs even after a fresh level up directly in front of said NPC and a skill level low enough that even the lowest trainers could theoretically train me.
I'll edit later to add a full mod list in case this is a mod conflict or something.