Howard Miller

While Iomad is closely related to Moodle, it is not Moodle. There are many changes.

You would be better asking in their Github issues. The guys over there are generally helpful.

I would start with... https://docs.moodle.org/404/en/Category:Tags

The page will be different because the search page will return anything with 'debug' in it. For example, plugins may have a debugging option. Depends on your setup.

Unusual, I would think - but my best guess is that something is "tipping over" a security setting in the web server. Nothing that can be fixed in Moodle.

I would expect the web server logs should give a more detailed explanation of why those pages have been blocked.

If you're lucky, this could also explain the other problem you are having.

I think you need to be clear what you mean by "Developer mode". There's really no such thing.

I assumed you mean "Theme developer mode". Which, from the above, doesn't make much sense.

Are you perhaps confusing Developer mode with Debugging mode? The latter might make sense for investigating an email problem. I'd also be surprised if Debugging mode caused the problem you are seeing.