I switched from Verizon to Fi and back and now I can't send texts to certain people

[Android Central Question]

I am normally a Verizon user but am about to travel internationally so I signed up for Project Fi to use while abroad. I have a Nexus 5X. I activated the Fi SIM, with a new phone number, and texted someone whom I have previously texted from my Verizon number. That text sent fine, however when I put my Verizon SIM back in and again texted the person, the texts now will not send. I can still receive texts from them, and call them. I can also text anyone else that I did not text from the Fi number. All the texting was done in Android Messenger. I assume the issue stems from using two numbers in the same text thread. Thoughts?