[Resolved] Server memory crash

Dear support Team,

I hope you are feeling well because this one is a tricky one.

Context

I'm a professional WordPress developper for 10+ years. I have made a WPML+WooCommerce webshop 2 years ago using your plugin. Everything was fine since a few weeks.

The website is in french (native language), with two other languages: English and German. For now, only the English part is translated, the German part is pending some translations.

WordPress and Plugins used on this website are on "auto update" mode.

The problem

From a few days, the server is running out of memory when trying to view the english part of the website. After lots of research and test, I see that it occurs only when I activate a third party plugin: Extra Product Options & Add-Ons for WooCommerce -> aka "EPO" (link on CodeCanyon:hidden link) AND WPML String Translation. Only if BOTH are activate:
- if EPO is activate and WPML String Translation desactivate, no problem.
- if EPO is desactivate and WPML String Translation is active, no problem.

The problem can be replicated on a standard environnement. Switch to basic WordPress theme (twenty-three) or to Storefront by Automattic :the problem occurs. All plugins desactivated except the necessary WPML plugins, WooCommerce and the EPO plugin (all are up to date): the problem occurs.

The problem only happens on language with translated product that use EPO plugin. In this case, English is a secondary language, product using EPO plugins are translated. The english part of the website is broken. Note that it is all the pages, even the one not querying products.

Language with product using EPO plugin that are not yet translated, seems fine (German for example).

First I check with EPO plugin

So I get in touch with EPO plugin support. They pointed out that the error is coming from WPML String Translation.

So it's from WPML String Translation

While, yes, when you disable the EPO plugin, you can see the english part of the website, however even when EPO is disabled the server still returns the same message.

Fatal error: Allowed memory size of 671088640 bytes exhausted (tried to allocate 323584 bytes) in .../wp-includes/functions.php on line 5349

This error is also trigger when try to view the settings of the string WPML String Translation plugin at hidden link

Sandbox environment

The server configuration :
Apache server
640 Mo of memory allocated, which is quite fair and should not represent a bottleneck i think.
timeout : 60 seconds, which is also enough. The crash appends within 10 seconds.
Max input var : 3000, not sure why this should be higher for this type of website (not so many products).
Running PHP 8.0 and MariaDB 10.4

I have duplicated the original website and everything is ready for you to check.
Could you tell me how to send you the credentials? And if you need more than an admin access to the backend (FTP access, Database accces, ...).

If you want more precisions or a close follow-up from my side, I'm here to assist

Thanks for your precious help.