Problem with empty store page after downgrading MAgento 2.4 to 2.3.5

Question

Due to a payment provider that shall remain nameless not yet updating their extension to be 2.4 compatible, we've had to downgrade a new store from 2.4 to 2.3.5

The process wasn't particularly painless, but we now have the site functioning in pretty much every capacity EXCEPT that:

1. accessing the store (catalog) page results in an empty page (NOT a literally blank page, HTML with head and body tags loads but no content so a white page

2. products can be searched for using search but attempting to click through to the product page results in a 404

(We also had to downgrade PHP to 7.3 too)

What's weird is that even with Debug mode on:

• there is no error in console when accessing the store page
• there is nothing in debug.log
• there are no PHP errors in the PHP error log

We've switched from our custom theme to the regular blank one, and Luma, and the same thing happens

Caches have been cleared etc. basically the full 'deep refresh' via CLI:

php  bin/magento setup:upgrade
php  bin/magento setup:di:compile
php  bin/magento setup:static-content:deploy -f
php bin/magento indexer:reindex
php bin/magento cache:clean
php bin/magento cache:flush

Has anyone experienced anything similar in the past, and can tell us where to go next?

Or at the very least, can anyone suggest how we can at least get some error messages telling us where to look?

Answer 1

Although I didn't stumble upon this issue, the first thing I would check is to make sure that you are loading the application from the same location set in app/etc/env.php as well as the DocumentRoot/ root directive in your webserver (depending on what you are using, Apache or nginx).

Answer 2

I'm sorry to say that Magento doesn't support downgrade. However, if you still want to do it, you need to install Magento version 2.3.5, create a fresh site then migrate data from your old store to the new one.

Answer 3

To close the loop on this, in the process of attempting to create a test product, an error was thrown referring to a missing class from the Temando_Shipping module

This module was no longer being used, but it turns out that there were product attributes still in the database referring to this.

After some brute force searching in PHPMyAdmin I managed to track all of these down and just deleted them (the module was already removed)

This allowed me to save the test product and the store page then started working, listing just this product.

When I then went in and just saved the other products ready on the store that seemed to do whatever was needed to get them showing as well.

Why there was no error information when the page was trying to load I still don't know, but hey ho...