Looks like @Tam might be busy for a bit. She is better at this kind of thing than I am but in the mean time here are a couple things to try / think about.
1. When you start getting that "taste" after the 20 ish hits, pop the top of the atty and check the cotton. Specifically next to and in the coil. Is it well saturated? The limitless has a long distance to wick and if the cotton is too thick they can dry out a bit. If the cotton is getting dark brown or black it is singing. That makes for a bit of a nasty vape.
2. The limitless produces a lot of fog. Do you think your mouth could be drying out? Lots and lots of water while vaping is the answer to that. Personally, I'm weird, diet coke does it for me.
3. If your wicks are cut high, are you tilting the atty long enough between vapes to allow the cotton to wick properly.
I guest last thing I can think of, which is a long shot, is this a new liquid? It may just have an after taste that comes through after vaping a bit.