HELP, Passport Automatically Deleting Messages

Hello,

My passport recently deleted a text conversation with two different people at two different times.
It was important information I needed. I left my phone for an hour, came back and the person's new text message was where the conversation started. And the previous conversation was gone :(

Can someone please explain me what is happening and walk me through a solution on how to keep messages forever on Passport unless I delete them.

Cheers.

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