Can not ping compute engine VM

I posted this answer to make this issue and a way to avoid it more visible.

As it was confirmed at the comment section by GaryB, this issue was caused by IP changes after resizing the VM instance.

You can find more information about this behavior at the documentation Ephemeral external IP addresses:

An ephemeral external IP address is an IP address that does not persist beyond the life of the resource. When you create an instance or forwarding rule without specifying an IP address, the resource is automatically assigned an ephemeral external IP address.

and

For VM instances, the ephemeral external IP address is also released if you stop the instance. After you restart the instance, it is assigned a new ephemeral external IP address.

To avoid such situation, you can follow the documentation Reserving a static external IP address:

If a virtual machine (VM) instance requires a fixed external IP address that does not change, you can obtain a static external IP address for that instance by using one of the following options:

• Reserve a new static external IP address and then assign the address to a new VM instance.
• Promote an existing ephemeral external IP address to become a static external IP address.