What you were expecting to happen, and what actually happened:
I completed the Task Brawler by winning 85 battles. Then I played several additional battles to see if these would count towards the next level after collecting.
After I collected the 20 chaos shards, the next level showed my progress at 0/170 battles.
How often does this happen? When did it begin happening?
Today with the new Campaign.
Steps to make it happen again
Play any battle until the task is completed, then play extra battles and collect the reward afterwards.
I tried the match heroic gems one, and progress did continue. After claiming the bronze level, I started the silver level with progress already made.
Seems to be working for some tasks, but not others.
Claimed the first level of one task, think it was brawler, and it was at 2, even though I’d fought more than 2 before claiming (been playing for like 20 minutes of battles before claiming). It was like it still kept going, but only a little bit. Weird.