Watch OS 2 - What do the spinning dots mean?

On my Watch OS 2 application - it's a simple tableView that shows 4 pictures - I'm getting the six dots spinning - when the application first loads and occasionally while the application is running (after a user action).

1. What are the six spinning dots referred to as?

2. What's causing this behaviour. I think the application is reasonably straight forward and cannot see that the issue could be performance related... I do initiate the picture downloads as background processes and that uses NSURLSession.

[[NSProcessInfo processInfo] performExpiringActivityWithReason:@"Fetch images from www" usingBlock:^(BOOL expired) { ... }];

I've run myself out of places to look. :-(

- David