DateTime being persisted to one DB column but not the other in Symfony 4.4 app

Question

I have a baffling issues where I have a DateTime object which seems to be able to be persisted and flushed to one column, but not the other.

I have checked the DB, the data isn't be written to the "protectiondate" column.

$lifecycle->setRemovalDate($extendedProtectionDate); // this line works
$lifecycle->setProtectionDate($extendedProtectionDate); // this line doesn't
$em = $this->doctrine->getManager();
$em->persist($lifecycle);
$em->flush();

The fields are defined identically:

    /**
     * @var DateTime
     *
     * @ORM\Column(name="removalDate", type="date", nullable=true)
     */
    private $removalDate;

    /**
     * @var DateTime
     *
     * @ORM\Column(name="protectionDate", type="date", nullable=true)
     */
    private $protectionDate;

As are the accessors and mutators:

   /**
     * @param DateTime|null $removalDate
     *
     * @return Lifecycle
     */
    public function setRemovalDate($removalDate = null) : self
    {
        $this->removalDate = $removalDate;

        return $this;
    }

    /**
     * @return DateTime|null
     */
    public function getRemovalDate() : ?DateTime
    {
        return $this->removalDate;
    }

    /**
     * @param DateTime|null $protectionDate
     *
     * @return Lifecycle
     */
    public function setProtectionDate($protectionDate = null) : self
    {
        $this->protectionDate = $protectionDate;

        return $this;
    }

    /**
     * @return DateTime|null
     */
    public function getProtectionDate() : ?DateTime
    {
        return $this->protectionDate;
    }