$PAC team is currently investigating an issue with some wallets going onto a different chain. At this stage, there is nothing to be concerned about, as this seems to have been a temporary problem. The new 51% penalty system has done its job in ensuring the correct chain retains control over the network.

Currently one does not believe a 51% attack was attempted. It seems to be more of an issue with a mining pool investing significantly more hash into the project, due to increased demand/profitability and thanks to the new reward structure.

If you find your wallets unable to sync, please reindex your 12.6.0 wallets and check you are on the correct block height.