R6020 blocking access to certain websites

Hi.

I am getting "This site can’t be reached" <website> took too long to respond. errors, only on certain Russian websites.

If I plug my network cable directly into my modem, thereby bypassing my AC750 router, I can load the site/sites just fine. I can also load these sites using mobile networks (4G/5G). I can only guess that my router is blocking my access to these sites. By restarting my router or turning certain settings off (and on again sometimes), I can *sometimes* load these sites. 

There are no traces of my router blocking these sites in the router log.

I do not want to depend on resetting or restarting my router to solve issues. How can I permanently fix issues like this? Is this a known issue? I am running the latest firmware version and do not have any other issues.

Sorry for the double post, but my router falls into both categories.