Whenever I set the longitude and latitude of a point I want to insert and click on 'Save' I lose everything. I can't set and save a 'home' area either - when the map is published it centres on a place in Vietnam!? There is an error "No result was found for this address: " displayed under the map.

There are no user guide materials or documentation in the zip file package I downloaded for me to reference - so the instructions in the module are incorrect.

I'm using Joomla v3.5. in a DEV environment, so you won't be able to see it.

Am I being an idiot by not doing something obvious?

Hello, thanks for using our module!
we do not see this error ever, could you please check for js issue or upload to host.
I'll check and fix it.
Regards,
Kien

I'm using your module in Joomla within an internal DEV environment to choose a CMS (and modules) for a new website. Unfortunately there is no way to make it accessible to the public so you can access it.

Running the console (F12) in IE11 causing the browser session to crash, so I can't see if there are an JS errors. The issue is to do with saving the settings in the module; they just disappear after I have saved the changes, the map re-centres on Toronto and all items inserted are removed - it basically resets itself.

I'm not a developer, so I'm not experienced enough to start modifying code. If you haven't seen it before then I guess it must be something else - I'll try a similar mapping module and see if that has the same problems.

Really very hard for me to be able to help you. I can not recreate this error fixed.
Could you please try again download and reinstall module.