You know, I did see that nice, easy-to-read green button there that says, "Solve Database Problems." It looked very inviting, and I came close to pressing it before, but since I had involved you all in this process, I didn't want to take a chance it could potentially mess up any step you would have preferred I try first before pressing it.

But, since it seems you gave me to go-ahead to do so now, this morning I pressed it. After a few seconds when finished "percolating" ... the screen cleared and then came back up with the green affirmative message:

"No Problems Found in Database" 

Whoah! :-)

I of course quickly went and tested out search again, and it seems to be working just fine now! Excellent!

Thank you all for making this fix so incredibly easy! If I had only known to look in that "tables" page on my own. Now I know. ;-)

Thanks for the help @robert and @chris!

I think this is a database MariaDB 10.1 bug with "full text" index. First check if there are any db error in Dashboard > Forums > Tools > Tables Tab. If there isn't then try to delete "full text" indexes in wp_wpforo_table then create them again for the title and body fields. Use phpMyAdmin database manage plugin or the one in your hosting cPanel.

Now, even when searching for a single word that I know is in almost all posts, using the "Search Entire Posts" method, it always returns zero search results and the message "Posts not found."

(Attached screenshot showing what a basic search looks like with this message)

My membership and forum is targeted at helping people with their photo collections, so searching for the single word "photos" should pull up nearly every post when searching using "Search Entire Posts."

However, of note, when searching using "Find topics by tags", then I DO see results just fine. I tried other search type options and the only other one that does bring search results is "Find Topics Started by User." All the others also show no results.

Troubleshooting Steps:

I copied my website to a staging area on my Cloudways host, deactivated every single plugin except the wpForo plugin and wpForo addons, and still no search results with "Search Entire Posts."

I turned off Varnish (server-side caching) and still no search results with "Search Entire Posts."

I changed my Wordpress theme from Divi to a stock Wordpress theme and still no search results with "Search Entire Posts."

I then deactivated all wpForo addon plugins, so only the wpForo plugin and default wordpress theme were running, and still no search results with "Search Entire Posts."

I'm sorry, I can't share a link to my forum here in this forum since mine is a private group. I could share access to my forum in my staging area by sharing credentials through DM or email etc. with support.

I was hoping this amount of information might be helpful (enough) if support in here has already helped someone in the past with a similar situation.