I’m not sure whether it was caused by my recent upgrade from WordPress 3.9.x to 4.1, but I noticed a considerable drop in sales the day after the upgrade. After checking my website on my iPad I noticed I got the message “Page cannot be displayed” or actually since it’s a dutch website “Deze pagina kan niet worden weergegeven”.

Testing the WordPress upgrade

Since several components of my site were outdated I set-up an testing environment which is running with another hoster. I tested the website after updating a couple of plugins (17 updates were needed). Most did not cause any problems but most important was the woocommerce 2.2 update, and the update of my export tool (Store Exporter) since this is what I need for running my shop. 

There where no mayor issues, the only thing was that my category pages were not working, but after ‘saving’ the ‘permalinks’ settings it was fine.

Since I had really strange (for me serious) issues with store exporter in the past, and I really rely on it’s functionality for exporting my shop orders I am really cautions updating anything that might break the export.

But after update all plugins I updated WordPress to 4.1 (finally). All worked well and I was confident that at the end of the day (00.00) I could update my main website / webshop without expecting any issues.

Upgrading my WordPress website

As expected, the upgrade was not causing real problems except for the fact that when I tried to update several plugin at once (I had tested them individually already) the process stopped and got stuck in maintenance mode.  Since I have had the same issue before the fix was easy.. as is everything once you know it 🙂

After finishing the update I run some basic test, placed some dummy orders and all seemed fine.

The day after upgrading

In the afternoon I got worried since the number of orders were lower as I expected but since orders were placed the website seemed to be working, until I checked my website on my iPad. I got worried.

Page Cannot be displayed

I got “Page cannot be displayed”, looked like the website was not available but on my phone the site was working.. I checked on the computer and all seemed fine as well until I tried Internet Explorer (I use Chrome by default).

So it looked link safari (on my iPad) and Internet Explorer had some kind of issue with my website. Since my website was constantly visited by (potential) customers I obviously did not want to shut it down for maintenance, and I could not find a solutions via Google.

I tested my test website via internet explorer which seemed to be fine, which I think was very weird but there were minor differences as the database content for example had not been updated for a few weeks.

Due to the minor differences I decided to backup and restore the current website to my testing environment.. but still, my test environment worked fine. I checked all settings, even PHP versions running on the server I made sure were the same..

I was pretty hopeless and could not explain why it was working on the one site.. and not on the other site, maybe some settings on the hosting? I still don’t know.

The solution

After midnight the site visits stopped so I decided to do some testing on the main / live website. WordPress sites not running properly is often caused by a bad plugin, but since al was working fine on my test environment I did not expect a plugin to be the problem, but since I was running out of options I decided to disable plugins in little groups.

I put the site in maintenance mode I started disabling the last couple of plugins. I refreshed the website in internet explorer and voila.. website showed up.. after enabling the plugins one after another I found the plugin that caused the issue: WP HTTP Compression

Still I’m really confused why this didn’t work on my live website and why it was no problem on my test website but I’m happy to have found the cause, and since the plugin was not really needed (www.webpagetest.org didn’t show any difference when enabling / disabling the plugin) disabling this plugin was a no brainer..

Steps in finding a solution

Google

Usually the first thing I do when having an issue is Google.. I Googled in dutch and I Googled in English but somehow I could not find any similar issues with WordPress site. I Googled “Page cannot be displayed” and “Deze pagina kan niet worden weergegeven ” but no useful results showed up.

Validate website

I used validator.w3.org to check my website. This is what I noticed: The working website on my test environment had far more issues then my live website!

Webpagetest

I used www.webpagetest.org to test my website using different browsers for testing. This is something I intent on doing more often in the future to prevent same thing happening when update my site in the future!

Copy  / Clone Website

I downloaded al files using FTP and made a database backup using Updraft-Plus backups, I purchased the cloned add-on previously which is a great tool for only a few dollars. It allows me to restore a backup from site X to  site Y, replacing all the correct links (I used to do this manually with a search and replace.. but that’s a hassle and error prone).

Disabling plugins

After all other failed and it was midnight and there were no more active users I started testing on the live website. I put it in maintenance mode (by Seedprod) to do this and started to disable a couple of plugins.

Luckely I then found the ‘bad’ plugin and got rid of it.

Reading up on the WP HTTP Compression plugins comments I noticed that some said that this plugin also caused the plugin update progress to fail, which might be the reason I got stuck in the (default WordPress) maintenance mode!

 Any corrections, remarks or additional information? Please leave a comment!