Vanguard bug exists still even on Mystel on some form.
If you enter Ace dungeon, you get vanguard rewards only once. Second runs gives no vanguard rewards, so you lose gold, xp, ep xp and vanguard credits it would give. You have to enter Pit of Petrax, Ghillieglade or some multi-player dungeon to get them back.
Vanguard Requests have been bugged least since fall 2020 on NA servers. Around the time when Gameforge took over NA they became bugged on EU too. There seems to be some fixes. On NA 2020 you literally had no quests at all unless you entered a dungeon.
Nowadays we are only missing 2nd quest of the day, and some daily quests you finished yesterday are not reset properly.
Also it seems if you remove and equip a weapon or other gear (item level changes) you sometimes don't get all the dungeons vanguards you should. This is fixed when entering dungeon, but you have to do it from instant matching menu, not on vanguard menu.