How do I delete this long conversation?

[AC Question]

I have a long running group conversation with three other friends. It's gotten to be QUITE long, to the point where, for the past two or three weeks, it might take upwards of 15 seconds to load the conversation. Assuming it was how long the conversation was (because it doesn't happen to any other conversations), I decided enough was enough and attempted to simply delete the conversation with the hopes of starting a new one. Unfortunately, after sitting and waiting for the 'Deleting' screen for about two hours, during which I couldn't use my Message+ app, all of my messages never got deleted. Instead, every message text was replaced with "Unsupported Attachment." It still takes 15-20 seconds to load all the unsupported attachments, too, so the problem wasn't fixed. I did some googling and couldn't find another instance where this happened to somebody else. The conversation is still functional, and I can receive messages and send messages no problem, with the message texts reading fine, but attempting another delete simply does the same thing, replacing the huge history of messages with a bunch of "Unsupported Attachments." I don't want to do a factory reset on my phone, is there another thing I can try to fix how long it's taking to load the conversation? I don't care about any histories of conversations at this point, I just want to be able to open the app and talk to my friends without waiting almost a half minute.

 

[Seronac]

Try going into Settings/Apps and clearing the cache data for Message+, or uninstall and reinstall it.