I guess this issue is gameplay issue for me. Some completed Kingdom tasks are hidden for me. I looked at known issues and Bug reports board and couple ones there:
Some Kingdom task do not trigger until the next time you upgrade one of those troops, open a chest etc.
[known issue] Is anyone else having the problem of Kingdom tasks not updating?
were not like the issue I see. For example, there are 3 uncompleted tasks displayed in task list and if I complete one, for example I upgraded 12 kingdom troops to level 5. Then I clicked on the “Collect all tasks” button and new uncompleted task appeared and I had again 3 incompleted tasks. Then I upgraded kingdom class to level 20, collected task rewards and after that appeared next task, complete tier 2 trial battle, which was already completed. I collected rewards from that and again completed task, collect legendary troop, appeared which was already completed. After I collected rewards from that task I again have 3 incompleted tasks. And it happens with every kingdom I complete some task. As I have completed trial battles up to tier 4 for all it also makes me wonder if there are rewards for completing tier 3 and 4 trials and they sit somewhere waiting until I complete specific tasks and reach to them. Is this how kingdom tasks work? You complete them but get rewards only after you have completed certain tasks before them?