TT74 on "[Plugin: W3 Total Cache] Showing 404 when tested with GTmetrix"

I agree, I was vague. I guess I'm just annoyed that the plugin author hasn't provided any answers/support for a long time. In my eyes this plugin is slowly decaying.
Yes, this problem occurs mainly on GTmetrix Canada location. If I run test on Pingdom via US servers, many of the tests go okay but eventually I'll get 404. Again, that has never happened before. My main audience is in the same country that my server is located, so no problem there, all good.

To answer your questions Destac

Did you misconfigure the plugin?
No changes to plugin setting has been made for over a year.

Did you ask for support regarding the plugin?
Answered above.

What caching modules are you running?
Page cache: disk enhanced
Minify: not in use
Database: Opocode:XCache
Object: Opocode:XCache
Browser cache: enabled
No CDN
All settings are a combination of theme authors suggestions with tweaks fo my setup suggested by my host, and they have served me well. I have applied the PHP7 correction that Kimberly has shared on this forum earlier.

Site is running on shared server Apache CGI/FastCGI. PHP 7.0.4, MySQL 5.6.15, WP 4.5.1.

What is the website URL?
http://www.rar.fi

Any insight that you might provide is greatly appreciated.