Hiya MC12345678!!!

Fresh install of EP4 on clean install of Zen 1.5.8 and php 8.1:

First issue I had was the blank page... made the private to public change noted above in query factory but it did not fix blank page.
Checked error logs and there is some issue with ep4 error logging folder...

So I un-commented line 97 of easypopulate_4.php:

Code:
 $ep_debug_logging_all = false; // do not comment out.. make false instead This is now controlled from admin.
and was able to run the EP4 installer.

I created a couple directories and test products with sub-categories manually.
Exported a FULL EP4 file, and turned around and was able to import and all "updated" correctly.

I then manually deleted these products and categories from the admin and re-ran the import and received this:

SKIPPED! - v_products_model: TEST_Model - No category provided for this new product
SKIPPED! - v_products_model: TEST_Model_2 - No category provided for this new product

Haven't looked any deeper yet. I'm going to have to sweep the cobwebs out of my brain and look at the code again. Been quite a few years since you adopted EP4! Glad to see you are still taking good care of it!

Almost 3500 posts! Holy Cow!