Few WAF Rules (Fortinet Rules) are blocking web requests whenever I save a page

I believe Fortinet wont share what is exactly inside these rules, even if you contact them. You can try to request that, but it is not guaranteed they will provide that info. In that case, you would either have to disable that specific Firewall Rule, or, if possible, inspect the GET/REST request the application is making, and try to see why it triggers the Deny from the WAF rule (and perhaps adjusting the code so it does not trigger it).

The last option is perhaps to look into different WAF managed Rules that wont block your Web requests (and there are many others to choose from)