I'm having a the exact same issue. It stated this morning and seems to be only happening on mms messages, like any group text or picture message. When I switch to the stock android app the problem dissappears, as soon as I'm back on Messages+ it begins again. I've force closed and erased the apps data and cache but the problem comes right back as soon as I start it up again. Perhaps this is a system issue if it's affecting multiple users.