Last night, I walked 1.25k and had the last Portkeys I needed to finish the Brilliant Event bonus at 2.7k. I got up this morning with an hour left in the event and went out to finish unlocking the Portkeys and completing the remaining 1.75k I needed for the bonus.
After I had gone 2 miles along my route, I thought it was weird that I hadn't heard the Portkeys unlock, so I got out my phone and saw that the walking distance was still at 1.25. I started stopping and restarting the game while walking, and finally it went up to 1.36 - after I had walked about another quarter-mile.
I kept restarting the game and finally, after I'd gone about 4 miles total, the Portkeys unlocked when I reopened the game (for the sixth or seventh time) and the walking distance started tracking normally. But by that time, there were only 2 minutes left in the event. Considering it was raining the whole time, I'm obviously not very happy about not having gotten the bonus items I earned. This also isn't the first time I've noticed my walking progress wasn't being tracked properly. There have been times I've had Portkeys only go up .1k when I've walked over a mile.