500 Error! WP Site crashes with PHP Fatal Error

@dodgehat Would you be able to get your System Status Report from WooCommerce > System Status and paste it here?

### WordPress Environment ###

Home URL: https://caisafety.com/2016
Site URL: https://caisafety.com/2016
WC Version: 3.1.0
Log Directory Writable: ?
WP Version: 4.8
WP Multisite: –
WP Memory Limit: 256 MB
WP Debug Mode: ?
WP Cron: ?
Language: en_US

### Server Environment ###

Server Info: Apache/2.4.10 (Debian)
PHP Version: 5.6.30-0+deb8u1
PHP Post Max Size: 64 MB
PHP Time Limit: 30
PHP Max Input Vars: 1000
cURL Version: 7.38.0
OpenSSL/1.0.1t

SUHOSIN Installed: –
MySQL Version: ? 5.5.55 - We recommend a minimum MySQL version of 5.6. See: WordPress requirements
Max Upload Size: 64 MB
Default Timezone is UTC: ?
fsockopen/cURL: ?
SoapClient: ?
DOMDocument: ?
GZip: ?
Multibyte String: ?
Remote Post: ?
Remote Get: ?

### Database ###

WC Database Version: 3.1.0
WC Database Prefix: wpsite_
woocommerce_sessions: ?
woocommerce_api_keys: ?
woocommerce_attribute_taxonomies: ?
woocommerce_downloadable_product_permissions: ?
woocommerce_order_items: ?
woocommerce_order_itemmeta: ?
woocommerce_tax_rates: ?
woocommerce_tax_rate_locations: ?
woocommerce_shipping_zones: ?
woocommerce_shipping_zone_locations: ?
woocommerce_shipping_zone_methods: ?
woocommerce_payment_tokens: ?
woocommerce_payment_tokenmeta: ?

### Security ###

Secure connection (HTTPS): ?
Hide errors from visitors: ?

### Active Plugins (27) ###

Accordion Slider: by bqworks – 1.5.0
Add Meta Tags: by George Notaras – 2.11.3
AfterShip - WooCommerce Tracking: by AfterShip – 1.7.0
Contact Form 7: by Takayuki Miyoshi – 4.8
Custom Field Suite: by Matt Gibbs – 2.5.9
Duplicate Page: by mndpsingh287 – 2.3
Enable Media Replace: by M?ns Jonasson – 3.0.6
WPBakery Visual Composer: by Michael M - WPBakery.com – 5.2
Login Logout Register Menu: by Vinod Dalvi – 1.0
MailChimp for WooCommerce: by MailChimp – 2.0.0
New RoyalSlider: by Dmitry Semenov – 3.3.4
Scripts n Styles: by unFocus Projects – 3.4.0
Search By SKU - for Woocommerce: by Matthew Lawson – 0.6.1
Select Core: by Select Themes – 1.3.1
Select Twitter Feed: by Select Themes – 1.0
Simple Sales Tax: by Simple Sales Tax – 5.4
Booster Plus for WooCommerce: by Algoritmika Ltd – 1.1.0
Woocommerce CSV import variable products: by Allaerd Mensonides – 3.0.1
Woocommerce CSV Import: by Allaerd Mensonides – 3.3.5
WooCommerce FedEx Drop Shipping Pro: by IgniteWoo.com – 2.2.13
WooCommerce Google Analytics Integration: by WooCommerce – 1.4.3
Booster for WooCommerce: by Algoritmika Ltd – 2.9.0
Woocommerce quotation: by Aldaba Digital – 2.6.5
WooCommerce UPS Drop Shipping Pro: by IgniteWoo.com - Custom Add-ons for WooCommerce! – 2.4
WooCommerce: by Automattic – 3.1.0
Wordfence Security: by Wordfence – 6.3.12
YITH WooCommerce Wishlist: by YITHEMES – 2.1.2

### Settings ###

API Enabled: ?
Force SSL: –
Currency: USD ($)
Currency Position: left
Thousand Separator: ,
Decimal Separator: .
Number of Decimals: 2
Taxonomies: Product Types: bundle (bundle)
external (external)
grouped (grouped)
simple (simple)
variable (variable)

Taxonomies: Product Visibility: exclude-from-catalog (exclude-from-catalog)
exclude-from-search (exclude-from-search)
featured (featured)
outofstock (outofstock)
rated-1 (rated-1)
rated-2 (rated-2)
rated-3 (rated-3)
rated-4 (rated-4)
rated-5 (rated-5)

### WC Pages ###

Shop base: #5998 - /fall-protection-store/
Cart: #5990 - /cart/
Checkout: #5992 - /checkout/
My account: ? Page does not contain the shortcode.

### Theme ###

Name: Startit
Version: 2.3
Author URL: https://themeforest.net/user/select-themes
Child Theme: ? – If you are modifying WooCommerce on a parent theme that you did not build personally we recommend using a child theme. See: How to create a child theme
WooCommerce Support: ?

### Templates ###

Archive Template: Your theme has a woocommerce.php file
you will not be able to override the woocommerce/archive-product.php custom template since woocommerce.php has priority over archive-product.php. This is intended to prevent display issues.

Overrides: startit/woocommerce/cart/cart-shipping.php
startit/woocommerce/cart/cart-totals.php
startit/woocommerce/cart/cart.php
startit/woocommerce/cart/shipping-calculator.php
startit/woocommerce/checkout/form-billing.php
startit/woocommerce/checkout/form-checkout.php
startit/woocommerce/checkout/form-pay.php
startit/woocommerce/checkout/form-shipping.php
startit/woocommerce/checkout/review-order.php
startit/woocommerce/checkout/terms.php
startit/woocommerce/checkout/thankyou.php
startit/woocommerce/content-product.php
startit/woocommerce/content-single-product.php
startit/woocommerce/content-widget-product.php
startit/woocommerce/emails/customer-completed-order.php
startit/woocommerce/emails/customer-new-account.php
startit/woocommerce/emails/customer-note.php
startit/woocommerce/emails/customer-processing-order.php
startit/woocommerce/emails/customer-refunded-order.php
startit/woocommerce/emails/email-addresses.php
startit/woocommerce/emails/email-customer-details.php
startit/woocommerce/emails/email-header.php
startit/woocommerce/emails/email-order-details.php
startit/woocommerce/emails/email-order-items.php
startit/woocommerce/emails/email-styles.php
startit/woocommerce/global/form-login.php
startit/woocommerce/global/quantity-input.php
startit/woocommerce/loop/loop-start.php
startit/woocommerce/myaccount/dashboard.php
startit/woocommerce/myaccount/form-login.php
startit/woocommerce/myaccount/my-address.php
startit/woocommerce/myaccount/view-order.php
startit/woocommerce/order/order-details-item.php
startit/woocommerce/order/order-details.php
startit/woocommerce/single-product/add-to-cart/external.php
startit/woocommerce/single-product/add-to-cart/simple.php
startit/woocommerce/single-product/add-to-cart/variable.php
startit/woocommerce/single-product/add-to-cart/variation.php
startit/woocommerce/single-product/meta.php
startit/woocommerce/single-product/price.php
startit/woocommerce/single-product/product-image.php
startit/woocommerce/single-product/product-thumbnails.php
startit/woocommerce/single-product/related.php
startit/woocommerce/single-product/share.php
startit/woocommerce/single-product/tabs/tabs.php

@dodgehat Thanks for providing that, nothing really stands out as wrong.

I spoke with the developers and they mentioned that since this is not with every page load, there may be some sort of load/unload or caching problem at the server level causing this.

Just to rule out possible incomplete or outdated files, please completely remove the plugin and then load it again through Plugins > Add New. Once this is done, please let us know if you still receive the fatal errors.

Thanks. I will try that and get back to you on this Asap.

Okay, this seems to work for now. I encountered a few ‘Choose another card’ at checkout even though I was using Sandbox valid Test cards, but works if I enter a test card manually. I will keep monitoring and let you know. Thanks again for your help! ??