Text notifications but no new texts on phone

This has happened twice. My phone died. When I charged it and powered it back on I had multiple new text notifications. But when I went to look at the texts there were no new texts.

Last time this happened I texted the people who sent them because I had a feeling it was them, and they sent me a screenshot of all these new texts they had in fact sent me, however none of them ever showed up on my phone.