At the end of November my Deco M9 began blocking streaming music through Amazon Prime Music and TuneIn. I went through a few rounds of troubleshooting with Amazon without success until I got the idea to remove parental controls that had given no problem before.
It seemed to be a change to the parental control "online communication" that started blocking these streams. Apple podcasts, news, and weather all worked. Taking off that parental control restored my streaming music. I still block most others to avoid Amazon from tracking me with new features without my knowledge.
Sometime around December 15, 2020, pertaining to use on an IPhone with IOS 14.2 a Target app stopped working, TD Ameritrade's login function does not appear, and even TP-Link's help does not load. Once I bypass the router's advanced features with a VPN, like I am now, these features work. They are all the latest app versions.
I have used the parental controls to block invasive trackers, like google analytics, Facebook graph, Facebook pixel (plus about 10 of the the Facebook servers that appear). The only blocked categories from the Deco options enabled are gamblinh (could not post with the correct spelling) and pay to surf. Again, even TP-Link was being blocked!
I have used the Deco M9 plus for over a year with no such problems. These only developed since the end of November. It is possible the coding called by the web sites fails to load due for the blocked calls since even removing all categories did not solve the problems.
I use the Deco in router mode from a Verizon FIOS router and use the modem/router for DNS. The Verizon FIOS uses Couldflare's DNS 184.108.40.206. I block a few ranges of Chinese IPs on the FIOS Actiontec router. My Deco uses an Ethernet connection to the Actiontec and I believe I set it up to pass all connections except TV to the Deco. Whether or not the Actiontec is bridge vs. router has never been a problem.
I pulled one device off parental controls altogether and this restored most. I cannot swap to the blocked sites setting now since I connected to this site via the Deco app, but it is only about a dozen servers blocked, most of which are Facebook servers (pixel.facebook.com, graph.facebook.com, graph.instagram.com et al.) plus "Facebook" as Deco defined it. Yet, why is it blocking Target, TD Ameritrade, and even TP-Link?