Most obvious example is Firefox. The Debian Project allows Firefox to update outside the packaging system, automatically, at the whim of Firefox.
And there's the inclusion of non-Free software in the base install, which is completely against the Debian Social Contract.
The Debian Project drastically changed when they decided to allow Ubuntu to dictate their release schedule.
What used to be a distro by sysadmins for sysadmins, and which prized stability over timeliness has been overtaken by Ubuntu and the Freedesktop.Org people. I've been running Debian since version 3, and I used to go _years_ between crashes. These days, the only way to avoid that is to 1) rip out all the Freedesktop.Org code (pulseaudio, udisks2, etc.), and 2) stick with Debian 9 or lower.