speed capped

I need some help with the settings on my router. I'm pretty much a layman when it comes to networks though, so despite my best attempt at finding a solution online, I've not been able to. I have had my ISP send out engineers to the house to check the internet as I pay for Gigabit speeds but...

So the story of my router is, i got a speed of 400mbps from our internet service provider. before, i was able to get 400 something from my router through wifi for whatever reason, i am not sure whether this happens before or after an internet issue with our service provider i then notice my...