I've had my Archer C7 for a long time now, and have noticed that it may be blocking certain requests. This just started recently, even though I have not changed anything regarding my setup for a very long time.

tl;dr question: I'm not very tech saavy. How can I troubleshoot this further?

Here are the details that makes me think something changed specifically with the router, but I'm not sure how much of it is relevant.

Recently, two apps started hanging only on my Android devices: the Dunkin Donuts app, which doesn't get past the splash screen and Cryptomater, which I use to encrypt some files in Microsoft cloud storage. When I try to unlock my files, the app also hangs.

I sent a log file to the Cryptomater team and they looked at my log files and said that it was hanging because the cloud service provider was not providing a response to the request to log in, and that was what was causing the app to hang. They suggested it may be because my home network is blocking specific domains, but couldn't provide further help.

Sure enough, if I disconnect from my home WiFi provided by the Archer C7, both apps work fine. Both apps also work fine if I connect to a VPN first, and then use them on my home network's WiFi. They both hang only when I'm connected to WiFi without a VPN. 

Thus, it seems like something about my router changed and now it's blocking select domains, causing certain Android apps to hang. However, beyond setting up some basics and changing my DNS to CloudFlare on the router, I haven't changed anything concerning the router for a long time. Yet these problems only started happining in the past few weeks.

I logged into the router and I have no parental or access control settings enabled, and never did, so I'm at a loss why this started happening.

Any insight into how I can troubleshoot this further and possibly solve it would be greatly appreciated!