[wix-users] MSI asks for credentials to remove existing products

[Adan]

I have a windows desktop software that requires administration rights to 
install. The software is capable to auto-update itself if it finds an 
MSI with higher version than its own.
To do this new installation, there is an encrypted file with credentials 
for an administrator on the domain and the following steps are followed:

- The software will run a command to advertise the MSI with the 
credentials provided in the file as admin. (msiexec /jm path...)
- Then, with the current user logged into windows, it will run a command 
to install the MSI. (msiexec /i Path...)

It has been working well for many updates but in the last update, in 
some machines only, Windows Installer is asking for admin credentials to 
the user to remove the existing version. Instead of just showing an 
elevation prompt without login requirements.
There is no change in the wix xml file and the upgrade section is as follow:

<MajorUpgrade Schedule="afterInstallInitialize" DowngradeErrorMessage="A 
newer version of [ProductName] is already installed."/>

The verbose log does not show error before the un-install, just after 
the user cancells. It just comes with a need for credentials:

MSI (s) (60:AC) [18:41:10:512]: MSI_LUA: Elevation required to install 
product, will prompt for credentials
MSI (s) (60:AC) [18:41:27:782]: MSI_LUA: Credential Request return = 
0x800704C7
User cancelled installation.
C:\Windows\Installer\556ebd8.msi
CustomAction  returned actual error code 1602 but will be translated to 
success due to continue marking
Action ended 18:41:27: RemoveExistingProducts. Return value 2.

And it also shows that the user in use is indeed the admin from the file 
with credentials.

Could someone please lead me in a direction? I though 
RemoveExistingProducts action runs with server privileges.
The other thing that is frustrating me a lot is the fact that t works in 
some machines well.

Many thanks!