If I create an RBF transaction using the Qt GUI but specify my own custom change address, bumpfee doesn't work because it claims it can't find the change address:

    "Transaction does not have a change output"

This is because none of the outputs satisfy

    pWallet->IsChange(...)

I see there's a "TODO" commented in `CWallet::IsChange()` in `src/wallet/wallet.cpp`:

    // TODO: fix handling of 'change' outputs. The assumption is that any
    // payment to a script that is ours, but is not in the address book
    // is change.

I tend to put all my addresses in the address book whether I'm going to use them as change or not. I guess if the wallet was capable of creating its own SegWit change addresses I'd stop using custom change addresses, but currently it always seems to send change to a legacy address if I don't manually specify a change address.
},
    };
    if (solving_data) {
        args.push_back({"solving_data", RPCArg::Type::OBJ, RPCArg::Optional::OMITTED, "Keys and scripts needed for producing a final transaction with a dummy signature.\n"
        "Used for fee estimation during coin selection.",
            {
                {
                    "pubkeys", RPCArg::Type::ARR, RPCArg::Default{UniValue::VARR}, "Public keys involved in this transaction.",
                    {
                        {"pubkey", RPCArg::Type::STR_HEX, RPCArg::Optional::OMITTED, "A public key"},
                    }
                },
                {
                    "scripts", RPCArg::Type::ARR, RPCArg::Default{UniValue::VARR}, "Scripts involved in this transaction.",
                    {
                        {"script", RPCArg::Type::STR_HEX, RPCArg::Optional::OMITTED, "A script"},
                    }
                },
                {
                    "descriptors", RPCArg::Type::ARR, RPCArg::Default{UniValue::VARR}, "Descriptors that provide solving data for this transaction.",
                    {
                        {"descriptor", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "A descriptor"},
                    }
                },
            }
        });
    }
    return args;
}
void FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& fee_out, int& change_position, const UniValue& options, CCoinControl& coinControl, bool override_min_fee)