paperwhite 3 text display problem

I've been using the paperwhite 3 for awhile now, though I'm still new to it as an e-reader. Since I previously used a Sony and most of my files are in epub format, I've been converting most of my ebooks to the AZW3 format using Calibre before putting them on my paperwhite.

From the beginning I noticed an odd problem. Every few pages or so a line shows up where the words don't justify properly. An empty space about ten characters in length now and then appears on a line of the page moving inward from the right margin. At first I thought maybe this was just a quirk with one or a few ebooks, but I've since come to realize it's universal. Seems to happen with every book I read, including those downloaded in AZW3 from Amazon itself, which leads me to believe the problem isn't with the conversion but a bug in the way the reader displays text.

The only thing I can come up with is that Amazon has not fine tuned the reader software, and so it does not justify correctly with all font sizes. I am not using a very large font size, but it is a bit larger than the default font for the reader.

Don't know if this is really the source of the problem, but hoping to get some input from other users.

Has anyone else experienced this problem and is there any way to fix it?

Thanks for your help.