Is there anything I can do besides a factory reset?
Here are the factory reset instructions: Perform a Factory Data Reset (Device Powered Off) Prepaid LG Optimus Exceed 2 | Verizon Wireless
Stock messenger or Verizon messaging app? If the former, factory reset or try deleting all messages. If the latter, uninstall and reinstall, or rather, uninstall and never use again.
It's whatever came with the phone. Unfortunately I tried deleting messages this morning because I was having the "unfortunately messenger had stopped" all the time and after clearing most of the messages, that's when it quit.