Okay, im going to attempt to answer this as a 30 year old male currently on a dating app. Double messages are okay as long as they arent reaking of desperation. If you double or triple up a message because they each include their own seperate thought that ties into the conversation, or continues on the conversation, then thats a good thing. Also, the timing of your messages. If theyre all sent around the same time, good. If theyre sent like 2 days apart and its because the other person never responded, then youre starting to look desperate. One message after they havent responded for a while is okay (just to get a temperature check on how theyre feeling or whats going on) but anything after that makes you look like youve never interacted socially in your life, and will definitely scare people away.