RT-AC66R - Slow Navigating Router's Settings

I have an issue with my RT-AC66R running ASUSMerlin. I noticed that when I tried to change tabs within the router's settings the process is really, really slow. I tried resetting the router and cecking the logs and everything looks normal.

I can go to VPN > PPTP Server and it takes forever to get me to the setting page.

Anyone else had this issue before/now?

Thanks