I'm not sure if this is related to iOS 13 or if it's specific to dual SIM devices (I have 2 lines on my phone)...
I'm having issues where it will sometimes hang sending a message, or if I send one it will sometimes attach it to another person's thread in the preview area where all messages are listed. For instance, I can send a text to John Doe but that text may show up under Jane Doe's name in another thread when I view the screen that has all messages listed. If I open John Doe's thread, it won't have the new message. If I open Jane Doe's thread, it will show up in her thread. If I close messages app, it will show appropriately.
I'm having issues where it will sometimes hang sending a message, or if I send one it will sometimes attach it to another person's thread in the preview area where all messages are listed. For instance, I can send a text to John Doe but that text may show up under Jane Doe's name in another thread when I view the screen that has all messages listed. If I open John Doe's thread, it won't have the new message. If I open Jane Doe's thread, it will show up in her thread. If I close messages app, it will show appropriately.