I've been timing the freezes with a stopwatch, since I hadn't actually done that. Just noticed the time on my device, ie the app would get stuck and the digital time would be on the next minute by the time it got unstuck. With a stopwatch, I timed the app freezing for 15 to 25 seconds, and that's with me constantly tapping or swiping (trying to turn a page or bring up the table of contents, set a bookmark, or scroll up or down in browsing or change screens). It may not sound like much, but when you're reading a book and you get to the end of a page...it's a little annoying. And the app didn't behave this way before 3.9, so I know this app and service are capable of better.
Well, for now I'll deal with it as best I can. While browsing, I did come across a couple of books I want to read.