We had already identity the issue. We are running a job for this and will completed by this week.

Go to Active Directory > App registrations > New Registration
Name: [VSTS Name]
Accounts in this organizational directory only
Redirect URI (optional): https://VisualStudio/SPN

In this app registration go to Certificates & Secrets > Client Secrets

Add a new secret (any expiration, any description) after saved copy the [value] generated.

Go to subscription > Access Control > Add your app as owner
search for your[VSTS Name]

Go back to VSTS and select the option "use the automated version of the service connection"

copy Service principal client ID and Tenant ID from the AD

Service principal key is the [value] (Client Secret)

I have successfully fixed this, see my blog post: https://edi.wang/post/2019/2/13/fix-azure-devops-tf14045-error-when-deploy-to-azure

This is still a problem - I cannot add new service connections to any of our Azure subscriptions, nor can I manage any of the existing service connections. :(

I'm still getting this error. Was the fix deployed? I also can't even delete a key that I just created, or any others.

I found a workaround for this.
1) Go to this page and Go through all the points

2) And don't forget to run this script

The main idea is to get rid of this Auth window pop-up and specify all the data manually. (hacky way)

Sorry, here is the link

https://docs.microsoft.com/en-us/azure/devops/pipelines/library/connect-to-azure?view=vsts#use-spn