Planner Tab must be first reloaded

I used Graph API with C# and PowerShell to create a new Tab in a Teams channel and show inside it a Planner (that I also created and populated programmatically).

The problem that I have is that the first time I or a colleague open the tab, an error message is shown inviting me to click on help -> report problem (I do not have it) and to reload the tab. It doesn't matter if I open the tab in the Teams App or in a browser.

Once the tab is reloaded, everything works fine. For me and for others and every time.

I added a new tab with a website inside to see if the problem is general but this tab can be opened without problems. Only the tabs with Plans have this problem (every tab and every "first" time).

Do you know what the problem could be?

Thanks in advance for helping.