[Ethereum] BAD BLOCK and “invalid difficulty” error when syncing ropsten testnet in geth

I had been connecting to the ropsten testnet for the past couple months in geth with no issues, and able to quickly sync to the latest block. Now when I connect to ropsten as follows (as I've always done):

geth --testnet --syncmode "fast" --rpc --rpcapi db,eth,net,web3,personal --cache=1024 --rpcport 8545 --rpcaddr 127.0.0.1 --rpccorsdomain "*" --bootnodes "enode://20c9ad97c081d63397d7b685a412227a40e23c8bdc6688c6f37e97cfbc22d2b4d1db1510d8f61e6a8866ad7f0e17c02b14182d37ea7c3c8b9c2683aeb6b733a1@52.169.14.227:30303,enode://6ce05930c72abc632c58e2e4324f7c7ea478cec0ed4fa2528982cf34483094e9cbc9216e7aa349691242576d552a2a56aaeae426c5303ded677ce455ba1acd9d@13.84.180.240:30303"

geth attach

I get the following error every few minutes while it tries to sync:

[09-29|19:31:30]

#### BAD BLOCK ######### Chain config: {ChainID: 3 Homestead: 0 DAO: DAOSupport: true EIP150: 0 EIP155: 10 EIP158: 10

Metropolis: 9223372036854775807 Engine: ethash}

Number: 1700000 Hash:
0x279a2890d2b9d9c80da96d052173a5ea281417741aec6bc109efd1e779c2c83c

Error: invalid difficulty: have 11864637714, want 11858882854

#

In any case it's also only importing a handful of blocks a minute and it's only up to block 1731643 now, when at the time of writing ropsten is up to block 1769191 (so at this rate it'll never catch up).

I haven't found any information on the "invalid difficulty" error.