Messages disappear after phone restarts by itself...

Hi there, here are the specs of the phone:

iPhone 6 / 128 GB / 10.2.1 / Model: MG4R2LL/A

This past Sunday, I noticed my phone just restarting by itself. When I put in my passcode and went to send a message, literally ALL of my messages disappeared. I was surprised because nothing was going on with the phone (i.e. backing up, downloading, etc). The phone had been working a bit sluggish, but nothing like this. I proceeded with checking the storage information and it showed that messages ranked 2 with about 20+GB, which was lead by Pictures. I figured the messages were there since the phone could detect the storage.

I shut it off. Turned it back on, and still no messages. Then I got a message and it showed up on my messages list. But yet, the rest didn't show up at all! I looked to see what I could do. I did a hard reset, checked other settings, everything just kept showing up as if there were messages but couldn't be seen. As new messages showed up, those were the only ones on the list.

I decided to attempt to do a backup. After crazy headaches of telling me there wasn't enough space for a backup (even though there was 175GB free) I finally backed up the phone on Wednesday. Yesterday, after about four hours of restoring the phone to the backup, the only things that showed up were the apps (plus a few that had been deleted months ago), the messages that showed up after Sunday, lost all notifications settings, and apparently the 20+GB of messages data disappeared.

Can anyone help me out with any solution to try to get back all my messages I've lost? There are important messages from friends and family members that I need to have back.

Thank you in advance!