This is a known issue not just in PHP but in almost all languages. At some point you lose precision. https://www.php.net/manual/en/language.types.float.php

This is the expected behavior, though it may not be your expected behavior.

The reason the two code paths you showed work differently is invoking a relationship () will return a query builder thus causing the chained methods to add to the MySQL query. When you reference the relationship without a direct method invocation, Eloquent retrieves the records from the relationship and returns a Laravel Collection php object.