core: underscore in field name does not work with @Groups

Using camel case in variables only is mandatory to develop Symfony bundles or help in the Symfony project. If your project follow PSR-12 (PSR-2 is deprecated) you can choose what do you want for variable names. I always choose snake case and have use a lot of different bundles without problems since Symfony 2, and reflection works fine in all cases. I don’t know how this issue can be closed saying “if the behavior differs from the one expected by the property info” because is a completely correct way to define a entity in Symfony and Doctrine. I hope that you can reconsider your action and try to fix it. Meanwhile, if you have this problem you can use the groups directly in the setters o getters involved. You must change from

/**
 * @ORM\Column(type="int")
 * @Groups({"baz:read", "baz:write"})
 */
private $foo_bar;

to

/**
 * @ORM\Column(type="int")
 */
private $foo_bar;

/**
 * @Groups({"baz:read"})
 */
public function getFooBar(): ?int
{
    return $this->foo_bar;
}

/**
 * @Groups({"baz:write"})
 */
public function setFooBar(int $foo_bar): self
{
    $this->foo_bar = $foo_bar;

    return $this;
}

closing, use custom metadata if the behavior differs from the one expected by the property info as @teohhanhui said