AirPort Time Capsule is blocking access to specific website

I use AirPort Time Capsule as my router. Over the last days, I started updating my private homepage (using wordpress). After a while of doing this, I can not access my homepage anymore. Neither the configuration page of the ISP (which is on the same server).

Doing a hard reset of the router fixes it, but only for a few hours.

I did find similar problems from quite a while ago mentioning something wrong with the DNS settings. I tried using different DNS servers but that doesn't fix it.

Any ideas are highly appreciated! This behavior is just extremely annoying, and I can't wrap my head around the fact that it only affect a specific server I have been working on.

Thank y'all for your help.