Calling a function in the second loop returns unexpected value

I’m mapping my switches to a tool called Netbox which is a CMDB tool.

I have a list of switches for example: [US-switch01, US-switch02]
If those devices don’t exist in Netbox, I would like to create that device. Here is the script right now:

import pynetbox
nb = pynetbox.api(
    'http://netbox.domain.com',
    token='token'
)

devices = nb.dcim.devices.all() # An object of all devices in my Netbox instance
sites = nb.dcim.sites.all() # An object of all sites in my Netbox instance (EU, US for example)

def getSiteID(site):
    for s in sites:
        if s.name.upper() == site.upper():
            return s.id # Returns the ID of the site given to is. For example US site ID is 1. EU site ID is 2.

def getDeviceID(device):
    for d in devices:
        if d.name.upper() == device.upper():
            return d.id

if __name__ == "__main__":
    switch_list = ["US-switch01", "US-switch02"]
    for switch in switch_list:
        print(f"Working on {switch}")
        if getDeviceID(switch) is None:
            siteName = switch.split('-')[0]
            print(siteName, getSiteID(siteName))

When I run my script, I first test what it would find:

print(siteName, getSite(siteName))

So the above print should return siteName and the Side ID, which is what getSite() is doing.
The expected output is:

Working on US-switch01
US 1 #site name is US and the ID in netbox is 1
Working on US-switch02
EU 2 #site name is US and the ID in netbox is 1

For some reason, the output is this:

Working on US-switch01
US 1
Working on US-switch02
US None

Why do I get None as the returned value on the 2nd loop?

The weird part

If I use this list: [US-switch01, EU-switch01] then the script works:

Working on US-switch01
US 1
Working on EU-switch02
EU 2

So the issue seems to be when there are 2 consecutive switches with the same site. Why? What am I missing here?