Howard Miller

Remove the plugin (delete directory and files of the plugin). Almost certainly, the plugin is breaking the navigation structure.

Which plugin was it and are you *sure* it is compatible with your version of Moodle?

Either of those solutions works. It's up to you.

You can assign the Manager role to Course Categories to give them a degree of control over their own School. There are also Category level themes and so on.

The answer is probably a matter of scale. How many Schools and how much autonomy is required.

The logs report? Although, not everything you might think should be logged is.

I'm almost certain (I looked) that error is NOT being generated by Moodle. So, I think you need to look elsewhere.

The SSL proxy is the obvious candidate.

The post data to the web service API is (again) encrypted by HTTPS. So, still makes no sense whatsoever.