Ok I think this is worth posting.
So what happened is that I managed to finish a battle, and then moved to another Daily Plunder task. I entered the battle entry screen but for some reason backed out. After that, the soft lock happened.
FYI I am able to reproduce the soft lock by just going to the battle screen and backing out. Maybe this soft lock problem can be narrowed down to certain task groups? Today’s task that freezes is “Harvest Souls III”.
Another FYI, while I wrote that text above, the screen unlocked!! I managed to back out!