the T between vowels change to t͡s in some english speakers?
Usually when I heard "What's, that's" or similar constructions, where the T come with S, I always consider like a t͡s, so I really don't know if my ears need more train or if it is really a t͡s and a natural variation.
But there is other case, when I listen to some speakers, usually they produce the same sound, but when a T occurs between vowels.
So, better represented by /ˈbetə(r)/ sounds more like /ˈbet͡sə(r)/.
This variation often happen with speakers who use a soft T (more air flow out mouth) instead of a hard T.