Past iMessages not loading

I have an iPhone 5c with iOS 8.3

I've set my iMessages to keep messages forever. However, in one conversation I'm having the messages seem to be disappearing. We message daily, but when I try to review them it only goes back to so many messages before the recent messages stop and it shows messages from months ago (Example: It's Monday and I've messaged the person since Saturday. The messages only go back to Sunday and the one above it is from November). If I scroll to the top of the screen to load older messages, it sends me to the bottom of the screen. This same problem is reflected in the Attachment portions of the contact details. It shows old attachments briefly, and then loads the most recent attachments. But when I return to the message screen it still won't load older messages. I have my messages synced to my iPad, and I can review past messages if I've sent them from it. If I send new messages from my iPad, they still sync to my phone. But the messages I've sent on my phone from just last week seem to be gone. Any ideas for fixing this? Or has anyone else experienced this same problem?