I'm experiencing issues with DIM and D2 app as well. Nothing is loading.
DIM says I either have no connection or something is blocking it, I tried to disable all adblockers and other services/plugins on that website but to no avail.
D2 app just says "Loading failed. Check your network connection"
I can play the game just fine. No notification saying Im contacting servers or whatnot. No error code so far.