Unfortunately, I confirm the problem.
I have 1500 users in the database. When a guest vists the site, without logging in, it takes about 10 seconds to open each page. I have performed all the usual steps – changing the theme, disabling all plugins – to determine that the delay is caused by Page Restrict.
I looked into the code. In class-user-restrict-data.php, in the purchased_products_by_user function, there is strangely handled a situation when the user is not logged in ($user_id is false). Instead of returning an empty array of purchased products, it examines all users and their products. As a result, the code evaluated once for the logged user executes 1500 times for a guest. I commented it out, it helped. I recomend to review this piece of code.
