tendermint/tendermint#9468 introduced the ExecTxResult message type as a drop-in replacement for ResponseDeliverTx where it was used inside other messages. However, it did not carry over the options that explicitly set names for some of the fields:

  int64          gas_wanted = 5 [json_name = "gas_wanted"];
  int64          gas_used   = 6 [json_name = "gas_used"];

As a result, the JSON serialization of the structures containing ExecTxResult in RPC has changed in a backward-incompatible way.