Forum broken for Admin - Assets missing?

I’m having a problem when logged in as the admin on my production server. I think I may have caused it myself when I changed the app.yml value for DISCOURSE_S3_CDN_URL on the staging server to the same as the production server. I’ve since changed it back and the staging server is working fine just pointing to the S3 bucket. Looking at the browser console, it appears that some assets are not being found but I’m not sure how, why or even if this is the underlying issue.

Here’s an extract from the console when I try to access main forum URL:

I’ve tried safe mode but that doersn’t halp.

I’m still very much on the learning curve with AWS. I’ll continue to try and work this problem out for myself but any advice or guidance would be appreciated.