There are two ways you can use MCStacker Ad-free and more reliably. You could become a Patreon Supporter or you could buy the Deluxe Edition. Both of these methods should solve this problem. I understand that supporting the site in this way is not an option for some people and that's okay. I really want you to be able to use the site. To help you with this, I'm happy to give you this special link that sets a cookie in your browser which stops all advertising code from being loaded into any page on mcstacker.net for the next 24 hours.
I hope this works for you. If you try this link and MCStacker still doesn't work, it could have something to do with add-ons, plugins or browser extensions. Try an alternative browser to see if it helps. You can also try asking for assistance on the MCStacker Discord Server.