First bug: When completing Mirri's second quest, I expected to have to build up her rapport more before getting the third quest. But no, she offered it immediately. I know it was the third quest and not a second part of the second quest because on finishing it, I got the Mirri houseguest.
The final confirmation of this was that Bastian did not give me his third quest when I just now completed his second quest for the first time. I got his little gift, but he did not give a third quest. So I'm back to building up his rapport.
Also, second bug: Bastian's gift at the end of the second quest? Is that meant to be level-specific? The character I had was maxed out, but I got potions that were only level one Sips. I do have a single level 5 character right now (I made him to go through the Grand Unified Tutorial), but my 14 other characters are all leveled. And anyway, I would expect to get level 150 potions with a leveled character.
I am on PC NA. However, I have also reproduced this on my PS5 NA account as well. (I don't have Bastian there yet, but Mirri did exactly the same there.)
Been there, got the Molag Bal polymorph.