W3 Total Cache breaks ClassicPress, server error 500

[Atari-Frosch]

Me again.

• ClassicPress 1.4.1
• nginx version: nginx/1.14.2
• OS: Devuan Beowulf

Since 2022-06-28 02:25 UTC+2 my blog shows only blank pages, the page source is empty, too. All requests to https get server error 500. Requests to http are rejected by

        return 301 https://$server_name$request_uri;

as it should be.

error.log of nginx says:

2022/06/30 17:08:52 [error] 7365#7365: *2392332 FastCGI sent in stderr: "PHP message: PHP Fatal error:  Uncaught Error: Call to undefined function W3TC\wp_unslash() in /srv/$blog/wp-content/plugins/w3-total-cache/DbCache_WpdbInjection_QueryCaching.php:562
Stack trace:
#0 /srv/$blog/wp-content/plugins/w3-total-cache/DbCache_WpdbInjection_QueryCaching.php(507): W3TC\DbCache_WpdbInjection_QueryCaching->_check_request_uri()
#1 /srv/$blog/wp-content/plugins/w3-total-cache/DbCache_WpdbInjection_QueryCaching.php(424): W3TC\DbCache_WpdbInjection_QueryCaching->_can_cache_once_per_request()
#2 /srv/$blog/wp-content/plugins/w3-total-cache/DbCache_WpdbInjection_QueryCaching.php(123): W3TC\DbCache_WpdbInjection_QueryCaching->_can_cache('SELECT option_n...', '')
#3 /srv/$blog/wp-content/plugins/w3-total-cache/DbCache_WpdbLegacy.php(122): W3TC\DbCache_WpdbInjection_QueryCaching->query('SELECT option_n...')
#4 /srv/$blog/wp-includes/wp-db.php(2496): W3TC\DbCache_WpdbLegacy->query('SELECT option_n...')
#5 /srv/$(incomplete dir name!)" while reading response header from upstream, client: $IP, server: $blogurl, request: "GET /$article HTTP/1.1", upstream: "fastcgi://unix:/run/php/php7.3-fpm.sock:", host: "$blogurl"

Possible solution

I just found solutions that were very old and only applied to apache webserver. Or they demand that one logs into the blog, but that is not possible – the login page is also empty.

How can I get my blog back online?

[viktor]

The easiest option to bring your blog back online is to disable W3TC manually. Just go to your /wp-content/plugins folder, find w3-total-cache folder and rename it something else like w3-total-cache2.

They claim they support 3.8 version, so it should work. Unless there’s something else.

[Atari-Frosch]

Thank you! That did the trick

[viktor]

@Atari-Frosch what version of the plugin do you have? Apparently, they did have an issue but fixed it in the latest 2.2.3. Not sure if it’s related, but worth a check.

[Atari-Frosch]

It was indeed version 2.2.2. For the moment I removed it completely. If I find that my blog becomes much slowlier I might try installing it again. Or perhaps another cache plugin, I don’t know.