Can't send group message to a group of iPhones and non-iPhones

Recently when I go to respond to a group message that has both iPhones and non-iPhone users my message will not go through. I can still receive messages in that group but can't respond. I am able to iMessages fine (both to individuals and groups) and I can sent individual messages to non-iPhone users. In my messages settings it looks like I have my settings on to send MMS messaging and group messaging. Is anyone able to help me with this issue? Thanks!