Multiple SPI reads on Pi Pico requires reinitialisation

Question

I'm playing around with reading in analogue inputs from an MCP3208 ADC via SPI. However, reading multiple inputs seems to cause a seg fault unless I reinitialise the SPI on each read/write.

I've attached my 3208 interface code (which is heavily based off Adafruit's 3008 library). I haven't been able to setup a debug environment, so I don't have any insights on what goes on when it crashes. Is there anything I'm missing?

#include "mcp3208.hpp"
#include "hardware/gpio.h"

MCP3208::MCP3208(spi_inst_t *spi, int cs, int sck, int miso, int mosi)
{
    //spi_init(spi, 1000000);

    gpio_set_function(sck, GPIO_FUNC_SPI);
    gpio_set_function(miso, GPIO_FUNC_SPI);
    gpio_set_function(mosi, GPIO_FUNC_SPI);

    gpio_init(cs);
    gpio_set_dir(cs, GPIO_OUT);
    cs_deselect();

    _cs = cs;
    _sck = sck;
    _miso = miso;
    _mosi = mosi;
    _spi = spi;
    _baudrate = 1000000;
}

MCP3208::~MCP3208()
{
    spi_deinit(_spi);
}

void MCP3208::cs_select() 
{
    asm volatile("nop \n nop \n nop");
    gpio_put(_cs, 0);  // Active low
    asm volatile("nop \n nop \n nop");
}

void MCP3208::cs_deselect() 
{
    asm volatile("nop \n nop \n nop");
    gpio_put(_cs, 1);
    asm volatile("nop \n nop \n nop");
}

uint16_t MCP3208::scale(uint16_t scale_in, uint16_t old_min, uint16_t old_max, uint16_t new_min, uint16_t new_max)
{
    //Scales to 16 bit by default
    return (((scale_in - old_min) * (new_max - new_min)) / (old_max - old_min)) + new_min;
}

uint16_t MCP3208::read_adc(int channel)
{
    if (channel < 0 || channel > 7)
    {
        return 0;
    }

    uint8_t command = 0b11 << 6;
    command |= (channel & 0x07) << 3;

    uint8_t write_buff[3] = {command, 0x0, 0x0};
    uint8_t read_buff[3];

    // may need to fix this requirement to init then deinit deinit
    spi_init(_spi, _baudrate); //todo: remove

    cs_select();
    spi_write_read_blocking(_spi, write_buff, read_buff, 3);
    cs_deselect();

    spi_deinit(_spi); //todo: remove

    uint16_t result = (read_buff[0] & 0x01) << 11;
    result |= (read_buff[1] & 0xFF) << 3;
    result |= (read_buff[2] & 0xE0) >> 5;
        
    return result;
}