SharePoint Online - Issues with Modern UI

[Justin Taylor]

We're currently in the process of test migrating some site content to the new modern UI to get a feel for it and understand how it will impact users.

The list in question uses OOTB features it has 5 Site Content types from custom site columns, all inheriting from the Task content type.

However, I'm running into 2 major issues which are preventing us from even considering using the modern ui:

1. When we click a list-item's title to view the properties page, it instead opens a prompt to download a file instead of redirecting to the properties page:

   

2. When viewing the list item from the preview pane, the properties don't display because of a cryptic error that I cannot find info for on the web:

   Properties pane - modern UI

Until we can figure this out, we cannot even begin to consider adopting the modern UI. Anyone have any insights?

[#2]

We are also facing the same issue in the modern UI.

If the list (OOB) is in classic view everything works fine but when switch the list experience to modern UI user are getting prompt to save the file.

[#3]

Yep, having the same error text as others:

"Sorry, properties can not be displayed, having error: Unknown Error."

And clicking on list items prompt for download.

[#4]

Hello, we are having the very same problem here. We have migrated a task list from on-prem Sharepoint 2013 to Sharepoint Online using Sharepoint migration tool, and we have the same problem when switching to modern UI (clicking a list-item's title opens a prompt to download a file, task names are not displayed but a random number, properties not displayed). Any hint?