Pebble smartwatches are lots of fun when they are working. But it seems the latest update has caused some issues for some users. The Pebble 2.1 has bricked a few smartwatches, and users are not happy. For its part, Pebble seems to be working on a fix for the issue:
Today we experienced an issue deploying version 2.1 of the Pebble iOS smartphone app. We’ve pulled the update from the App Store for now. We’re working with Apple to fix this problem as quickly as possible, and will notify customers when an update is available that resolves the issue.
explained Pebble on Smartwatch Fans. If you have not updated your watch yet, you should wait till this issue is fixed.