wmts with basic authentication sometimes 401, sometimes 200

I have a secure wmts configured in GE 4.5.1\HTML5 2.6.1

 

Some of the web requests are returning 200 but others are returning 401 in Chrome.

 

If I open the URL that 401'd I'll receive the authentication challenge and the request

 

will work.

 

In IE11 I was prompted for a username and password originally which seems to have

 

worked as tiles are returning with 200

 

I've configured Web Tier configured credentials in service connections and also in the site

 

connections. I've also tried adding the username and password as parameters in the web

 

request but can't seem to consistently beat this prompt.