Block Text Messages - Quick Question

Hello, I have had the same problem happen with 2 unrelated accounts while traveling.  I enter a new contact and messaging just fine.  After a few days, the messages (on their end) say that I have blocked them and they can no longer respond to my messages.  I have checked my phone and their phone to make sure no one inadvertently blocked them with no luck.  Has anyone run into this and does anyone have a suggestion on what may be happening.  I don’t know the type of phone their using but I can find out if someone thinks that is helpful.  Thank you for letting me know if you have a solution.