Fade transition doesn't always work

I love the simplicity of this plug-in, but I am having an issue with the fade transition. The first couple of slides fade nicely into each other, but after that I lose the fade; it’s just an abrupt transition with a flash of white space in between. Any ideas what is going wrong here? I am using custom CSS, no navigation, so I have the following in my stylesheet:

.rslides {
  position: relative;
  list-style: none;
  overflow: hidden;
  width: 100%;
  padding: 0;
  margin: 0;
  }

.rslides li {
  -webkit-backface-visibility: hidden;
  position: absolute;
  display: none;
  width: 100%;
  left: 0;
  top: 0;
  }

.rslides li:first-child {
  position: relative;
  display: block;
  float: left;
  }

.rslides img {
  display: block;
  height: auto;
  float: left;
  width: 100%;
  border: 0;
  }

.rslides_container {
  margin-bottom: 0;
  position: relative;
  float: left;
  width: 100%;
  }

Thank you!

https://www.ads-software.com/plugins/simple-responsive-slider/