The bug allowed players to instantly reach the maximum in-game level. This would later lead to the crash of a game round. The developers have rolled back player ranks and released a patch to fix the issue.
Here is what community manager said about the patch:
"Due to Rank issues we've had with our max level players (auto-60, crashes at end-of-round) were resetting Rank stats for some players to alleviate the backend issue we have detected. Servers will go offline for roughly 30 minutes while this update is applied."
You can read the official patch text here.