SharePoint Modern list showing classic form only

 Another strange behaviour by SharePoint list recently required us to contact Microsoft support.

The list in question was created in a modern SharePoint Online site with default behaviour to show modern form. The list worked fine for a while.

And then suddenly it started showing the classic forms when creating or editing the list items instead of the modern forms.

Modern form:

Classic form:

First settings we checked was in the -> List Settings -> Advanced Settings to see if the list has reverted to Classic setting. All the settings were as expected. The settings were explicitly changed to 'New Experience' and default multiple times but it did not solve the problem.

Next thing to check was the -> List Settings -> Form Settings. Here it was noticed that the setting was default one, however it seemed that there was a PowerApps form published to the site at one time and then reverted to default form. Choosing the published powerapps form completely broke the list which basically indicated that it may be the cause of our ongoing issues.

Did contact MS support to help us revert the changes and as per them once the form is published, you can not revert this setting back. This later turned out to be incorrect as we showed MS on other lists that this is possible.

Next suggestion from support was to talk to PowerApps teams, which was a bit weird as this setting is in Microsoft.

While MS was trying to bounce our ticket back and forth between their engineers, we have tried to delete the PowerApps form (which was not recommended by MS), and IT WORKED. The list is now as good as new.

The link to delete the form is the last link in second option of the Form Settings.

Hope this helps and saves your time !!