Status bar could not find cached time string image. Rendering in-process

This bug/debug note is present in iOS SDK bundled with Xcode 9.3+

Update: not fixed in Xcode 9.4.1 (9F2000)
Update: not fixed in Xcode 10 (10A255)
Update: not fixed in Xcode 11 betas

I think you can safely ignore it. New versions of iOS/macOS sometimes contain informational debugging messages, and they generally get removed at the next release.

Same issue was occurring for me too. To overcome this, I did this

Goto Target -> Deployment Info -> Unchecked 'Hide status bar'

This one resolved my issue.For me, this was the 'Deployment Info' setup.

I am also seeing this warning appear, and in answer to Question 1, I am also seeing potentially very nasty behaviour associated with it.

Running something close to a basic sample animated triangle Metal app, but with

renderPassDescriptor.colorAttachments[0].loadAction = .load

such that the frame isn't cleared every frame. What seems to be happening is that every other time the warning message is logged, iOS also gets some part of its management of graphics state confused so that I witness a violent flashing of parts of the image (which then goes away again later).

How likely this situation would be to emerge in a 'real' app I'm not sure, but it's definitely not something you want users to end up seeing.

I haven't fixed the problem here thus far; 'Hide status bar' and 'Requires full screen' settings don't help.