Garmin Connect Web down?

It's not down. That link https://connect.garmin.com/modern/auto-challenge, is working for me. 

Perhaps try a different browser and/or clear the Internet cache? Is it just the auto-challange page that is giving you problems?

Thx for providing feedback. I tried different browsers, even on different devices. I just checked using Firefox and https://connect.garmin.com. Same result. There is a login page, but after entering my credentials, just an empty page shows up.

The cache ought to be empty since I didn't use Firefox for months.

What about on your phone using just a cell signal, not Wi-Fi? To see if there is an issue with your router and/or DNS.

Same result unfortunately.

Then I'm leaning towards an issue with your Garmin account. Is there someone near you that can test with their own account? Or you can create a new "test" account using a different email to see if issues persist.

Ultimately you'll want to contact Garmin Support.

With a new account, there are no issues

Ok then. I would contact Garmin via phone or chat.

Thx, I'll try to find out about the chat.

Chat and phone are not available, since I'm out of the office hours. I asked them by mail.

Email will work, but know that it will take much longer to get a resolution because they will ask many questions to get to the bottom of it. By then, it might start working anyway. 

It still doesn't work. I got an email that there is no solution available. I can partly see the web site when opening developer tools within the browser and removing one of the elements: