Something is blocking ads and I don't know what it is I am not complaining, it's awesome, but strange. I have a rooted Samsung a5, sm a500h, android 6.1.

Few weeks ago I installed adaway, and removed it because it couldn't block youtube ads.

And now the vast majority of apps don't display ads anymore, with the exception of musixmatch and youtube. I browse webpages using chrome, i see no ads on any website, including forbes.com and it let me in without complaining about an ad blocker, on tumblr, the ad space says "couldn't connect  to server x"

I did clean my device multiple times, using the likes of clean master, I did restart it multiple times. Is it possible that adaway did all that?
Somebody gone borked up their hosts file

Luckily, it's an easy fix. Your going to need root, and a root file manager (Like ES file explorer)

In your file explorer, go to /system/etc, and look for a file called 'hosts'. Open it, and remove EVERYTHING except the top line to disable the AD blocking. If you want to, of course

But why?

AdAway and similar apps use root auth to write to the hosts file the locations of ads. This then blocks them due to what said file does (it's a blacklist, essentially)