[5.x]: Website / CMS not accessible for all users on the same network

What happened?

Description

This might not be a bug but I am not sure how to label it.
Feel free to move it to wherever it fits best.

I am running a webshop with Craft CMS and Commerce for a store with 5 locations in different cities.
There is a lot of activity in the CP from employees that create manual orders or edit products, ...

The client has notified me that it has happened several times that the website seems to be offline for them.
However when I check the site it is online. It is also online for the other offices.
They can access other websites and when they check on mobile data the website also works.

At first I thought this had to be something network related.
But they don't have anything special configured.
No VPN's running or anything else.
This issue seems to fix itself after some minutes.

Could it be that because all devices on the network have the same public IP that they are also using the same PHP thread?
They obviously don't share a session because they all have their own accounts.
It might be that 1 user is triggering a process that locks up the whole thread that prevents all other users to access the website.

Is that last scenario something that is plausible or absolutely not and do I need to keep looking at network configuration issues?

Craft CMS version

5.x

PHP version

8.2

Operating system and version

No response

Database type and version

No response

Image driver and version

No response

Installed plugins and versions

No file, test, or entry point is identified. Start by reproducing the intermittent inaccessibility on the shared network and compare it with mobile-data access; done would require isolating whether the cause is Craft CMS, PHP request handling, or network configuration.