From roasbeef on Twitter:

🚨 attention lnd node operators that have upgraded or are considering upgrading to bitcoind 27 🚨

due to stricter validation for sendrawtransaction added in bitcoind 27 (https://github.com/bitcoin/bitcoin/pull/29434), transaction broadcast will fail if lnd is connected to a bitcoind 27 node: https://github.com/lightningnetwork/lnd/issues/8571#issuecomment-2060814517

the RPC code in btcd's rpcclient/btcjson library was using sat/KB rather than BTC/KvB (gotta love dem units) for the max fee value, this has been addressed in this PR: https://github.com/btcsuite/btcd/pull/2142 

we're planning on releasing an lnd v0.17.5 release to address this issue 

until then, you should hold off on upgrading to bitcoind v27 as transaction broadcast will fail otherwise 🙏