how do i debug a silent failure?

I’ve an issue with my site that is annoying me – and does not give any error.

To be specific, it is the image multi upload tool – I can upload images, they appear in the folders on my server, but my front end behaves as if nothing has happened.

There are no errors displayed or logged.  Devel doesn’t show anything as I am not submitted a page – I am only using functionality on a page.

I believe my code base is good, as I am running many sites on the same installation – and they don’t have this issue.

How do I go about trying to understand where the failure is?  What tools do I need?

Thanks

Richard

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