Who I have the same questioned this topic

Message+ on OSX was progressively getting less and less useful as new versions of OSX have been released after Sierra. It sync'ed fewer and fewer messages, hung when viewing a thread with images, and crashed several times per day. Now, it doesn't sync anything at all with OSX Mojave v10.14. I've uninstalled, cleared settings, and reinstalled.

Verizon - do you plan to update this app at all to keep up with new OS releases ?  It's completely unusable now.