Woo Commerce website errors

Our woocommerce site is constantly failing it has been fine for months but has suddenly started showing error and not allowing customers to use the site. We have carried out checks from the host provider and all is fine. The speed has also dropped dramatically. It’s proving hard to diagnose as it is not a constant issue it’s up and down.
The image below shows one of many error screens however the hosting company has checked and it is not hitting its maximum allowance.
Site is hosted on my20i VPS

Airsoftdirect.uk.com