Ok, I've managed to reproduce your issue. It is indeed a bug.
Fortunately, I see two solutions to your problem:
1) _ Reload a save prior to your final conversation with Llengrath (the one that triggers automatically when you teleport back to the Temple of Revelation after the final boss fight. So you ultimately want a save after defeating Wael but before transitioning to the main Hall)
_ Go back normally to the Temple of Revelation.
_ The dialogue with Llengrath should trigger automatically.
_ This time, cut to the chase and tell her right away that you have the artifact.
_ Do not give to her.
_ Your quest should then finish normally and you should be rewarded accordingly.
The issue only occurs when you first pass the dialogue, speak to her again and only then tell her that you have the artifact.
2) Less satisfying and completely barbaric, but you can use the debug command to reward yourself with the items you deserve.
Of course, be aware that this solution will lock further achievements. Therefore, only do this if you don't care about collecting them.
_ In the console, type "Iroll20s".
_ Type "giveitem LAX03_Part_Godseed_01"
_ Type "giveitem LAX03_Part_Godseed_02"
_ Type "giveitem LAX03_Part_Godseed_03"
And here you go.