In a recent update, we switched the blocking method from a deprecated method to the current, correct method. Unfortunately, it seems that the “correct” way is less dependable than the deprecated way.
In the next version of the app(estimated release by Monday 7/9), we will include a preference that will allow you to fall back to the deprecated method. The only downside to that method is that you must have a My Contacts group. A very small number of people don’t have this group, but we’re not sure why. It probably has to do with the minority of people who do not sync their contacts to Google.
As always thank you for the feedback!