Very slow load time on my checkout pages

Hello,

I'm getting slow load times on my checkout pages, and my host is saying it looks like there may be some theme issues with my recent update to PHP 7.4?

Example checkout page load time is about 11-15 seconds:
https://churchletters.org/cl-buygold?b_id=c75a2b

Here's their message to me:
I just checked and the best advice at this time would be to review the site's configuration with your developer. It seems that in this specific page (checkout), there are some syntax errors, as you can see in the following logs:

[09-Jul-2020 17:58:16 America/Los_Angeles] WordPress database error Column 'checkout_page' cannot be null for query INSERT INTO `wp_mvefqr_smartpaycart_an
alytics_checkout(b_id,checkout_page,visits,clicks,conversions,upsell,yes,no,yes_url,no_url,date,ipaddress,source`)
VALUES ('c525fb', NULL, '1', '0', '0', '0', '0', '-', '', '-', '2020-07-09', '46.229.168.140', 'default') made by require('wp-blog-header.php'), require_o
nce('wp-includes/template-loader.php'), include('/themes/generatepress/page.php'), get_template_part, locate_template, load_template, require('/themes/gen
eratepress/content-page.php'), the_content, apply_filters('the_content'), WP_Hook->apply_filters, do_shortcode, preg_replace_callback, do_shortcode_tag, s
pcShortcode, eval, smartpc_doStats

And

[10-Jul-2020 02:59:32 America/Los_Angeles] WordPress database error Column 'checkout_page' cannot be null for query INSERT INTO wp_mvefqr_smartpaycart_analytics_checkout (b_id, checkout_page, visits, clicks, conversions, upsell, yes, no, yes_url, no_url, date, ipaddress, source) VALUES ('dd3b5a', NULL, '1', '0', '0', '0', '0', '-', '', '-', '2020-07-10', '46.229.168.151', 'default') made by require('wp-blog-header.php'), require_once('wp-includes/template-loader.php'), include('/themes/generatepress/page.php'), get_template_part, locate_template, load_template, require('/themes/generatepress/content-page.php'), the_content, apply_filters('the_content'), WP_Hook->apply_filters, do_shortcode, preg_replace_callback, do_shortcode_tag, spcShortcode, eval, smartpc_doStats

Of course, upgrading your RAM will definitely improve your performance, but the main focus for this specific issue with your checkout pages are the logs shown above.

10:20:54 PM
This usually happens if you update your PHP version.

That could be the source of the issue. Some functions are deprecated or modified with each update, causing these type of errors.
10:23:13 PM
You might also want to review this with the theme's creator (GeneratePress).