The Chia team tested out the "Green Flag" drop on Friday 3/12 to simulate the change over from test to main net. The work difficulty was set too easy and it lead to a few syncing errors in on Windows and Mac machines.
If your wallet is not syncing with RC6 follow the instruction below to manually input the genesis block.
To work around on windows edit C:\Users\USERNAME\.chia\testnet\config\config.yaml and change testnet6: GENESIS_CHALLENGE: null to GENESIS_CHALLENGE: e0c271a9db2870e650a3634c58b52015c616ed90f1d47853cbbcd158df51a969
If you are using the Mac installer it is the same workaround but - Edit /Users/USERNAME/.chia/testnet/config/config.yaml and change testnet6: GENESIS_CHALLENGE: null to GENESIS_CHALLENGE: e0c271a9db2870e650a3634c58b52015c616ed90f1d47853cbbcd158df51a969
