Text Chain Delay

In the last 2 weeks, I have noticed a serious delay in sending texts. This only happens with text chains that include Apple and Android users. It doesn't happen on text chains with all Apple users, or single texts with either Android or Apple. Example: I send a text to a chain with an Apple and an Android user at 5:00PM and all users do not receive it until 5:00AM. It's usually at least a 10-hr delay. I thought people were ignoring me. But then I started getting the questions, "Why were you at Walmart at 3AM, sending pictures of things to us?" Of course, I was not, it was just THAT delayed.

I updated yesterday to iOS 11.3, thinking that would fix the bug, but it didn't. HELP!