... However, I will try turning off the autobackup feature in WP (which I have never had to use anyway) as I suspect it trying to autobackup to a hard disk that is turned off may be the trigger for the freeze-ups. I will report back on any result.
I doubt the WordPerfect automatic timed backup feature is the culprit since it does not activate unless there has been at lease one change made to the document while editing that document. We might presume the hard disk which stores this backup file (see below) is not turned off when you are editing and saving the document -- but if it is, then any save-to-disk operation, manual or otherwise, should start the disk spinning again (assuming it's not a SSD). If it didn't you'd be unhappy because the machine would appear "bricked".
The automatic timed backup (if enabled) would try to write a backup 10 minutes after a change (10 minutes is the default, but it can be changed). This seems to be a bit less than "a while". So I'm not sure it's a good candidate for the cause of your problem.
And too short a delay in auto-saving can present the problem of one backup not being finished before the next one begins.
It sounds to me like something else is at fault.
Just a guess: I suppose the disk on which the backup is made (specified in your program's Tools, Settings, Files, Document (tab), "Backup folder" field) might be on a network share that is not available, which might account for the program freezing. (Sometimes it can take several minutes for the computer to access the network.) If this is the case then it will be interesting for me to know so that I can update my site.
For more on the two WordPerfect automatic backup features see Automatically make back ups of your [WordPerfect] document to help you recover your work at http://wptoolbox.com/tips/AutoBAK.html. See especially the section entitled "With the timed backup feature enabled ... ".