URL referral doesn’t always apply the coupon discount

I’m testing the URL referral and I’ve found that it sometimes applies the discount at cart but not always. Are there any common reasons for this?

I have the website in 3 languages at the moment (using polylang). Can I make Spanish and French translations pages of the affiliate dashboard page or will this cause any problems? If that is ok, do I just choose the English version of the Affiliate dashboard page in the settings where I have to nominate a dashboard page?

Thanks for your time