Issue with assigning values to custom fields via API when creating a task

I have a script in Google Apps Script which creates Asana tasks. Over the weekend, I’ve noticed that some of the tasks that have been created are missing the custom field values that were assigned in the POST request.

After sending the exact same payload, multiple times, I’ve been unable to replicate the issue, although it has occurred several times. In my logs I can see the payload that was sent to Asana and the response. Everything in the response looks normal, except the custom field value was not assigned. Normally when an invalid custom field id is submitted, Asana throws an error and the task is not create but this is not the case here.

Could there be an issue with this particular custom field?