Question Problem moving a post from one category to another

Using Joomla 3.8.2, PHP 7.0.98, Kunena 5.0.12

Problem: I created a new Kunena category from the back end. On the front end, administrator opened a topic or post, clicked on Moderate, and tried to move it from its old category to the new category.

Result: Right after telling the move to proceed, the browser page went blank. I closed and opened the browser, logged in again, and found that no move had been made. (I did clear the cache). Then, Kunena and my whole web site slowed down so much that browsers (I tried three) started saying the website can't be reached because it was taking too long. Finally, I restored my site. (I had just backed it up). I repeated the Kunena post move procedure and my web site restore twice more with the same results. Finally, I restored my site one last time and left the Kunena post stay in its old category.

Has anyone had similar experiences, or have suggestions? Thank you.

I'm ok with leaving things as they are on my site, but I wanted to post this info in case it is a known problem, has a known solution, or it might help someone else.