Custom App (Static Tab) with SharePoint URL stays blank on first load in Teams Desktop Client

Hello Teams Developer Community,

We have deployed a custom Teams app (v1.25) that uses a Static Tab to display our company's SharePoint intranet portal. The contentUrl and websiteUrl point to our SharePoint site.

[The Issue] When a user clicks the app for the very first time in the Teams Desktop Client (New Teams), the screen remains completely blank (white loading screen). However, if the user clicks away to another app (like Chat or Teams) and then clicks back to our custom app, the SharePoint page loads perfectly.

[Observations]

This issue does NOT happen on Teams Web Client (browser). It loads instantly there.

Clearing the Teams Desktop cache does not solve the problem.

It seems to be related to WebView2 authentication/SSO redirect loops inside the iframe. I tried adding "showLoadingIndicator": true in Developer Portal, but the schema automatically strips it out upon saving.

[Question] Is there a specific parameter we need to append to the SharePoint URL, or specific domains we must add to "validDomains", to prevent this initial blank screen caused by auth delays in the Desktop Client? Any guidance on handling this WebView2 rendering delay would be greatly appreciated.

Thank you.