When a text field has the following changelog entry:

[
    'fieldId'    => 'customfield_10081',
    'from'       => null,
    'fromString' => null,
    'to'         => '',
    'toString'   => 'lorem ipsum',
]

Then its corresponding snapshot will be mapped to a list value. This value (an array) will be then cast as a string (since it is originaly a text field) and PHP emits a TypeError.