I've run into this issue a few times, and in all cases, I was able to solve it by simply adding a few more slides to the Swiper.

From what I’ve noticed, Swiper’s loop mode requires a minimum number of slides to properly clone the elements and build the loop structure. When there aren’t enough slides, blank spaces may appear between them.

My suggestion is to try adding more slides to the Swiper and see if the problem persists. Most of the time, that fixes it.