Hey Octopus, thanks for this. I really appreciate it...caniuse.com is a handy site.
Unfortunately, no luck. The problem occurs on iphone 6 using Chrome (which doesn't support hyphen control) but weirdly also occurs using IOS Safari (which does support it). If I use a browser emulator with the above device / OS, the problem doesn't replicate.
I'm injecting the code onto individual pages sitting under an index page, but not the index page itself. If I inject it into the index page, the text of the code appears at the top of the website (desktop and mobile).
Any other ideas appreciated! :)