So I went into that workflow and found the config for that node, and created an identical node in a new workflow (only difference being it uses my twilio credentials, and sends to my phone number) and constructed a virtual button payload to match what would be expected to go into the twilio node as you have it configured (down to even including a real dashboard url and sending to multiple numbers). The sms that was sent appeared correctly on both an android and an iphone.
One thought - if you log into your twilio account and look at your sms logs, do the messages look correct in there?
Side note, nice workflow! Even made me think of a potential twilio node improvement - being able to hand an entire array of numbers to the twilio node instead of having to set each number individually.