Version: 66.0.3329.0
Reproduction Steps: 
1. inbox.google.com
2. Press j to navigate to a bundle of messages, and open that bundle with the enter key.
3. Press j to navigate the messages, pressing x to select some of, or all of them.
4. Keep doing this past about ten messages, sometimes it doesn't take that long.
Expected: No matter how many messages I have in the thread, I should be able to keep navigating the thread without issue.
Actual: Eventually, by about the tenth message, and for sure after pressing more messages if there are more than 25 messages, Chromevox announces close, close, close, close, close... this repeats for a while, and eventually Chromevox unfreezes and I am able to navigate messages again. Sometimes though, Chromevox goes silent and the user is forced to cycle Chromevox off and back on.