Date format in PHP not working for me

Hello,
I have a CPT field called fish_datefirstsighted. It is a date field. When I display this using

<?php
    $value = rwmb_get_value( 'recapture_dateofsighting' );
    echo $value;
?>

I get: '2019-5-7' which represents 7th day of May 2019.

When I format as follows, I get 1 January, 1970.

<?php
    $value = rwmb_get_value( 'recapture_dateofsighting' );
    echo date( 'j F, Y', $value );
?>

I know this result means there is a date translation error but I don't know how to resolve this.

Can anyone offer a suggestion?
Thanks,

John.