Well I've reached lv81 before talking to Mjoll in Riften... And according to UESP pages it seems to require a level up to open up the dialog line from Mjoll. So I cant start her quest "Return the Grimsever".

Anyone ever did the same mistake? Known workarounds? (other than loading a previous save)

Most important of all: Anyone knows what are the quest that require a level up to start or progress?

I know that the wolf queen one also does, any other?

I was level 22 or 23 when I went to Mjoll to get the quest.For the first time, I hit this bug. I read the wiki before, but they all sound like they disagree on what to do. I had noticed when she told me about Grimsever the background would distort at the same place in the dialogue each time (I assume where the option to ask about Grimsever would be). I tried everything (reloading, waiting, etc.), even attacking her, to force the dialogue option, but no go.

So I finally talked to her and then stole some iron from the blacksmith to level up (I was nearly there). Upon leveling up I spoke with her again, and the dialogue automatically came up. I don't know if leveling is what actually causes the conversation to move forward, or if it's anything major that does it, but it did work for me. There was also another dialogue option that came up, but I forgot what it was.

I read that Grimsever sometimes doesn't spawn. I was worried that since I encountered the conversation bug, this might happen. However, the sword was where it was supposed to be.