Browser widget "Navigation request cancelled"/"NSURLErrorDomain error -999"

[Ben Rubinstein]

I'm finding intermittent issues with the browser widget failing to load an 
internal site.

In 9.6.8, the error (in browserDocumentLoadFailed) will usually be 
"NSURLErrorDomain error -999". In 10.0.0 (dp 5) it will be "Navigation request 
cancelled".

Alternatively, sometimes  (at least in 9.6.8) it will be
	"The resource could not be loaded because the App Transport Security policy 
requires the use of a secure connection."

... which is fair enough, because it's an "http:" URL rather than an "https:" 
(this is an application on our intranet); but the whacky part is that 
_sometimes_ I can load the site, and once loaded I can navigate it fine.

In particular I have more success in loading it in 10.0.0 (dp 5) - although 
sometimes the site will load, _and_ the browserDocumentLoadFailed message will 
be sent! I also sometimes find I can load it if I set the URL in the property 
inspector for the browser widget, where setting it in script fails.

Can anyone shed light? I'd prefer to get this working in 9.6.8, because due to 
https://quality.livecode.com/show_bug.cgi?id=24268 I tend to lose work in 
10.0.0 (dp 5) - but if I could get it consistently working in either that 
would be a step forward!

TIA,

Ben