PWA Project Site List Web Part Closed And Re-added - Datasheet View Disabled

On our PWA instance, we have a master template which defines the SharePoint Project Site layouts. On this template, we have a list web part, which is editable in Datasheet View.

On a particular project, a user closed the list web part. After re-adding it, Datasheet View is disabled. The tooltip reads - "This control is currently disabled. You might not have the right permission level to use this, you might need to select an object or item, or the control might not work in this context."

I've ensured that List Settings -> Advanced Settings -> "Allow items in this list to be edited using the datasheet" is enabled, and tried toggling it off and back on to no effect. I've also verified that I have permissions to edit the list - I'm logged in as admin.

I'm using IE9 and able to access Datasheet View on other projects (where the list web part wasn't closed) in the same IE instance, so it's not browser settings.