GetSystemIdForPublisher doesn't return unique ID

I use GetSystemIdForPublisher() to identify machine IDs. According to the documentation they are unique, but I have a handful of machines which return the same ID. These machines are completely unrelated and have no common history. They are located in different countries and belong to different users. The Windows version of these machines is the latest Windows 1909 10.0.18363 update.

The documentation clearly states:

The method will first attempt to use the Trusted Platform Module (TPM), if present, to get an ID. If a TPM is not present, the method will try to get an ID from the Unified Extensible Firmware Interface (UEFI). If neither of these sources is available, this method will return an ID that is backed by the Windows registry. In the case of the Windows registry, the ID will not satisfy all the above guarantees. For example, if a system does not have a TPM or UEFI support, and thus an ID was obtained from the registry, a clean install of Windows will result in a new, different ID being returned. Callers of this method should refer to the Source property of the returned SystemIdentificationInfo to determine where the ID was obtained from in order to understand the guarantees provided.

As far as I can see, none of these statements explain to me what is happening here. Does anyone else have an idea whats going on? Any help is highly appreciated!

Addendum:

we got feedback in form of a cpu-z report from 2 persons on 2 different continents with the same machine id:

user A:

Mainboard Model Z87M Extreme4 (0x00000444 - 0xECE9B6D4)
UEFI Yes
BIOS Vendor American Megatrends Inc.
BIOS MSG 63-0100-000001-00101111-1xxxx5-Chipset
BIOS Date 12/10/15
Mainboard Vendor 000001

user B:

Mainboard Model 151-BE-E097 (0x0000025D - 0x0A74C7F0)
UEFI Yes
BIOS Vendor American Megatrends Inc.
BIOS MSG 63-0100-000001-00101111-0XXXX5-Chipset
BIOS Date 09/10/15
Mainboard Vendor 000001

both got the same identifier when calling GetSystemIdForPublisher():

XlPRXXXlAPXk-yFXXXJUv3-XXXXXXXXXXXXX = [source is UEFI, ]
==> X included for obfuscation

We have around 60 customers worldwide whose computers return this exact ID.