Pie -- Won't Send Text to Specific Phone #'s / Double Texting

[Android Central Question]

Just upgraded to PIE and while texting to most #'s seems normal, however, I have an employee that I text with quite often, and the messages won't go through -- this has NEVER happened before updating to PIE. Additionally, I have a contact who says he keeps getting my messages twice -- never happened before PIE.

Anyone know of a fix for this?