ADM shows ssl certificate errors on some occasions for me too. Try use this download manager, it solved my issues with ADM. https://play.google.com/store/apps/details?id=idm.internet.download.manager This download manager is best alternative to ADM imo.
source, search, heart and pencil: the "heart" can be accessed from the menu. Press the 3 vertical dots then press "Bookmark" or "Remove bookmark". It fixed the problem for someone else with an android tv. I'll add source, search and pencil in that menu as well.
Calendar and MAL: I'll investigate. The list of series, latest, ... are working so I don't understand why these 2 don't.
android tv leanback launcher: do you mean this https://play.google.com/store/apps/details?id=com.google.android.leanbacklauncher&hl=en&rdid=com.google.android.leanbacklauncher ? I don't know what you want exactly but none of my devices are compatible so I don't know if I'll be able to do anything.