You can only train with him once per day and only at night
Once your stats are maxed out then he will no longer show up, and need to do the complete the second dungeon. Dialogue gives out a lot of information so it's best not to skip any dialogue. If you don't know how to engage the second dungeon just go to known locations in Ashton city. Fyi Patrik not showing up anymore isn't a bug, it's built in that way, The dialogue you missed was Patrik running off to dungeon himself, hince why he isn't showing up anymore.