Websites can require emergency maintenance for a couple of reasons

If the site has been hacked or is vulnerable to a security threat.

1

Security Breaches

When the server hosting the website crashes or is down. Shopify & BigCommerce provide their own hosting.

2

Major functionality of the site is broken or not working as intended.

3

Critical Bugs

The site is extremely slow or unresponsive, affecting user experience.

4

If there's a risk of data loss or corruption that needs immediate attention.

5

Data Loss

Issues with payment processing that could affect sales and revenue.

6

Essential software or plugin updates that could cause the site to break or become vulnerable.

7

Software Updates