There is a glitch on the Android app around blocking websites. I have an example of blocking YouTube.com. I had been trying that without success on the Android app, then I happened to login to BD central portal on my PC and added it there and boom, it worked. Perhaps BD can have a look at that or the community users can try it if you have other sites that can't be blocked or allowed.
However, it's not for all sites though, I have been using the Android app for 2 years and it mostly works.