Many people reported problems with either Liu-Fei‘s or Freya‘s quest, or both.
And that it seems to be impossible to do both quests simultaneously.
I might figured out a way to work around this.
I managed to progress with both quests at the same time.
Disclaimer: i play on ps5! So this “workaround” could possibly not work on whatever platform you might play. This workaround propably also won‘t work if you started one of the quest lines already.
(Maybe @Kikigirl could fit this information into your list of cutrent bugs and issues, sorry warrior princess but i couldn‘t read through all that 
…anyways)
WORKAROUND :
The trick is to simply start both quest lines, but to start with Liu-Fei!
It’s also very important to do Liu-Fei‘s tasks FIRST before you continue with Freya‘s quest line!
This way i was able to have both of them showing up at my improvised camp and i was able to interact with both of them.
However, sadly Freya‘s quest line is a bit longer. While i already got my Liu-Fei, i just went to new asgarth wit Freya what means i have to wait 8 hours for the finally against the bitch.
Of course i also started Liu-Fei‘s quest line again, but can’t deliver the ingredients because the Freya quest line is still going (i assume).
Of course FC needs to fix this stuff, but if this works on your end too it‘s propably a much better solution than doing them one after another. 
Additional tips:
Freya‘s quest line is longer but also buggier.
Sometimes she gets stuck (like after collecting the ingredients) or doesn’t follow you.
IF friendly fire is active just kick her, this will make her snap out of it.
If friendly fire isn‘t active lure a nearby enemy to attack her, this will make her snap out of it as well.
In new asgarth sometimes she stops following, in this case run back outside where you met her before and talk to her again.
To avoid that npcs attack Hagarth wich they unfourtunateley do, clear all the npcs nearby.
Also don’t attack Hagarth yourself and don’t have fighter thralls with you 
Otherwise he won‘t go in this down kinda state where you can talk to him, he will just die, Freya has to beat him in order to get him into this down state.
But even if he dies before you can talk to him, he should respawn if you run away out of render distance.
In the following videos by @Wak4863 you can see what our heroes are capable of in case you think they are useless. (Even though some of this will propably get fixed… eventually)
Would be nice if this helps some of you, and of course feel free to give some feedback if it works for you to progress with both quest lines.
Happy hunting 
P.s. If this turns out to be a reliable workaround it might be a useful information for the community @Wak4863
BUT:
