When I near the end of the pack and get to the similar sounds test, every day the trainer gets stuck on a handful of words and will go back and forth, often going back and forth between the same two words three or four times and sometimes repeating one word three or four times in a row. This doesn’t seem to match with your description of how the trainer works. Is this a bug? I’m getting them right, with only one or two errors each night, so I’m not sure why they keep repeating them.
The minimal pairs will definitely do that; I designed the trainers to give you a lot of exposure to each minimal pair the first time you encounter it, and then an extra burst of exposure whenever you get one wrong. If you find a pair really easy and just want it to go away, hit the 'Easy'/'Very Easy' button on the far right and you won't see it again that day.