Bug: Gmail tasks behaving weirdly after re-adding label

Imagine the following scenario. I have an email that I gave the akiflow label, then i answer that email and finished whatever I wanted to do and mark the task a done in akiflow. Everything fine so far.

But now I get a reply to my reply which is something I need to take care of as well so I mark the conversation (gmail afaik does not allow me to label a specific email within a conversation sadly) again with the akiflow label. This leads to some weird behaviour. The old task that I already completed is reopened in akiflow but a the same time there is a new one created in my inbox. So I have one on my calendar where it was originally planned and one in my inbox, still they are somehow linked because when I mark one as done this happens to the other one as well.

Is it possible to make the created task always refer to the latest email within a conversation?