Hm, I've found the error in logs here. Were you editing this in another tab before editing in this one? (Our logs are implying that one of these 2 pipeline actions, one that already existed, is deleted but you are trying to update it).

If not, just curious what was the loose actions you took that got you here? (e.g. just editing an action and clicking save)

This happens a lot when I try to edit something that already exists. So go edit a task, try to change it or add a subtask, then try to save it. Usually I give up, delete the whole stage and recreate it from scratch