6.42.7 bug still present for me too. As @hebertonlp describes, IPv6 works well for a long time. My PPPoE was up for over 24 hours with IPv6 working. Then I rebooted the Mikrotik and left the office. When I came back about 6 hours later, the IPv6 prefix was bound, but clients had no route to any IPv6 addresses. I again rebooted the Mikrotik and immediately logged in to Webfig. Although the PPPoE connection came up immediately, it was stuck on "Rebinding" the IPv6 prefix, but as soon as I hit the "Apply" button (without changing anything) it immediately obtained a prefix, and clients were able to communicate over IPv6.