AdBlock Problems

I don't have an answer for #2, but as to #1 i've noticed similar odd behavior regarding adblock in 18.06.1, meaning 3.5.5-3 is listed as an Available package, while also being listed as an Installed package, it persists even after updating lists and a reboot, so who knows, just an odd quirk (you might try updating lists or rebooting to see if 3.5.5-3 shows as installed).

edit - you might ask in the Adblock support thread, @dibdot is really good about answering questions and looking into things.