Web app doesn't load properly (UI looks like broken)

Hi folks,

I recently created a subdomain in Cloudflare and exposed my web application (hosted on VM in Azure) to the subdomain. The web app is accessible, works quite fine, but some pages can´t load (it just shows an empty page).

I never experienced this problem before. I also never used Cloudflare before.

This is the error I get:
x.domain.com | 520: Web server is returning an unknown error Error 520 Ray ID: 6962cc199b8242d5• 2021-09-29 05:26:33 UTC Web server is returning an unknown error You Browser Working Frankfurt Cloudflare Working x.domain.com Host Error What happened? There is an unknown connection issue between Cloudflare and the origin web server. As a result, the web page can not be displayed. What can I do? If you are a visitor of this website: Please try again in a few minutes. If you are the owner of this website: There is an issue between Cloudflare’s cache and your origin web server. Cloudflare monitors for these errors and automatically investigates the cause. To help support the investigation, you can pull the corresponding error log from your web server and submit it our support team. Please include the Ray ID (which is at the bottom of this error page). Additional troubleshooting resources. Cloudflare Ray ID: 6962cc199b8242d5 • Your IP: x.x.x.x • Performance & security by Cloudflare Error details

undefinedServer: x.domain.com
URL: /api/scannow.htm?id=2051
Time: 7:26:33

I found this case with the same app and problem: Cloudflare DNS Breaks PRTG UI | Paessler Knowledge Base.

Anyone can help me with this problem?

Thank you in advance.

Best regards

There have been a handful of 520 errors on sites (Search will turn these up). If none of their suggestions work, you’ll have to open a support ticket.

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