As far as I can recall, only three other users have reported such a problem before (in differing versions of Lightroom and the Juicebox Plugin) and two of these users reported that they were using Mac OS X 10.11 (the other user's operating system is unknown).
Please see these forum threads:
https://juicebox.net/forum/viewtopic.php?id=2115
https://juicebox.net/forum/viewtopic.php?id=2249

Please let me know what operating system you use (and also what version of the Juicebox Plugin you use) so that we can gather more data about the problem. If you are not already using the latest version of the plugin (v1.5.1), then I would recommend upgrading to see if this makes a difference.
The Juicebox Plugin for Lightroom can be found inside the Juicebox-Pro zip package and instructions for downloading the latest version of Juicebox-Pro can be found on the Upgrading Juicebox support page. (Instructions for installing the plugin can be found here.)

Unfortunately, I have never been able to replicate the problem myself on my own Windows 10 PC and it is difficult to troubleshoot a problem which I cannot reproduce.

When the problem next occurs, try reloading the live preview window by pressing Cmd+R (Mac), Ctrl+R (Windows) or by selecting 'Web -> Reload' from the drop-down menu at the top. Hopefully this will clear the problem.

Another workaround might be to prevent the live preview window from being updated each time a configuration option is changed and, instead, update the live preview window manually (whenever required) by pressing Cmd+R (Mac), Ctrl+R (Windows) or by selecting 'Web -> Reload' from the drop-down menu at the top.
Disabling the instant update functionality to the live preview window (and reloading the web page only on demand) should hopefully help (even though it might not be an ideal solution).

If you'd like to try it, download the 'galleryInfo.lrweb' file from here and use it to replace your plugin's existing 'galleryInfo.lrweb' file (inside the 'juicebox_pro.lrwebengine' folder/package). (This file should be used to replace the 'galleryInfo.lrweb' file in version 1.5.1 of the Lightroom plugin only.)

Please note that on a Mac, 'juicebox_pro.lrwebengine' is seen as a special package (rather than just a regular folder). To open the folder, you'll need to right-click the package and select 'Show Package Content'.

I hope this helps.