keplermanu

I managed to fix it. I’ll post the solution here for anyone else having this problem.
The problem I was encountering was this error in my error log

PHP Fatal error: Uncaught Error: Call to undefined function wp_get_current_user() in …/wp-includes/capabilities.php:693

I think pretty much all the function in the weight training plugin were getting called too early in the stack, which led to errors.

I fixed this by changing the contents of …/weight-loss-tracker/export/inc.php
from

<?php

defined('ABSPATH') or die('Jog on.');

require_once( 'functions.php' );
require_once( 'db.php' );
require_once( 'hooks.php' );
require_once( 'admin.page.php' );
require_once( 'activate.php' );

to

<?php

defined('ABSPATH') or die('Jog on.');

add_action( 'wp_loaded', 'load_plugins' );

function load_plugins(){
    require_once( 'functions.php' );
    require_once( 'db.php' );
    require_once( 'hooks.php' );
    require_once( 'admin.page.php' );
    require_once( 'activate.php' );
};

so all necessary code gets called after my other php files are called and not beforehand.
With this change everything seems to work ok for now and my css has returned back to normal.

If I rollback the plugin back to ver 7.6.4 I can use it without having troubles accessing my css files.