Zend certified PHP/Magento developer

Large Configurable: Failed to load resource: net::ERR_CONNECTION_CLOSED

Magento 2.4.5 p4 – Porto Theme – VPN with Cloudflare CDN and Imunify360

I’ve had this problem since upgrading to 2.4.5 p4 from p2, but downgrading does not help.

I have some configurables with upto 1000 simple products. Since my last upgrade I am unable to add any more simple products to any configurable with more than a few hundred existing products.

As soon as I click the “Add Products Manually” link, I get the “Something went wrong error”. and the system is unable to list products to be added (infinate spinner) There is no log information in Magento for the error or in mysql/php logs.

Smaller configurables do not get the problem.

Google console has shown me 2 differant errors.

Live site: Failed to load resource: net::ERR_CONNECTION_CLOSED
Test site: Failed to load resource: the server responded with a status of 414 (Request-URI Too Long).

Whilst we are currently experimenting with increasing the allowed url size on the server (A temporary fix only) this is a recent issue and large configurables have been not had this problem before.

I have seen several older posts reporting it as a fixed bug and other get/post discussions but nothing recent.

Through testing I have eliminated the following additional possible causes.

Imunify or other firewalls
Cloudflare
Cache
bookmark_ui
My PC cache: (I have tested on other PCs at differant locations with other firewalls)
Server changes
php settings

Currently at a loss as to what’s causing this.

Any help greatly appreciated!