New Relic will be retiring Synthetic Labels in favor of New Relic One Tags and currently the TF New Relic Provider does not have a resource for New Relic One Tags.
I reckon when Synthetic Labels are applied after the end of life the TF APPLY will fail. So my plan at least for my code base is to comment-out the Synthetic Label resources.
As of today, New Relic Synthetic Labels End Of Life Date is July 20, 2020.
We are currently working on a Provider v2.x, and should have an initial beta release out in the next few weeks. That release will add Entities / Entity tags and should resolve this as well. The issue for adding tag support is #656
Thanks for keeping an eye out @MAN98.
Related to #672 .
Resolved by #679