Unexpected behavior using SW vs. HW SPI on ESP32 with the SX127x LoRa module

So to be completely clear, this is what's not working for me 🙂:

const PIN_SCK = D18;
const PIN_MISO = D19;
const PIN_MOSI = D23;
const PIN_CS = D5;        // NSS
const PIN_RESET = D21;

// Configuration
const txConfig = {
    bandwidth: 0,
    freq: 434330000,
    power: 17,
    forcePaBoost: true,
};

// HW SPI (replace the three lines above)
SPI2.setup({ sck: PIN_SCK, miso: PIN_MISO, mosi: PIN_MOSI });
const sx = require("SX127x").connect({ spi: SPI2, cs: PIN_CS, rst: PIN_RESET });

// Poll DIO0 for interrupts
setInterval(function () { sx.onIRQ(); }, 100);
sx.setTxConfig(txConfig);

// Transmit
sx.send("Hello", function () {
    console.log("TX done");
});

(Edit: Perhaps I should try to remove the SX127x stuff, and boil it down to only using the SPI, I'll be back.)