Cloudflare’s ‘Auto Minify’ system is end-of-life, and will be removed imminently:
It does not support modern JS syntaxes, and therefore breaks Discourse’s code before it reaches the browser.
So I’m afraid there’s nothing we can do on the Discourse side to fix this. Cloudflare’s Auto Minify feature is broken and no longer supported 
The general advice is that minification should be done ‘at build time’ instead. That’s what we do at Discourse, and it might already be the case for your main website as well.
Here’s a discussion about the feature’s deprecation on Cloudflare’s own community:
https://community.cloudflare.com/t/deprecating-auto-minify/655677