Text messages to a specific person disappeared on iPhone, but not on iPad

Hi everyone, I recently found that all my text messages to a person I’ve regularly communicated with for many years have disappeared on my iPhone. I found through the filter option on my iPhone that I could recover some from the last month but the last five years with have all gone. None of the text messages to other senders, e.g. family members which I have communicated with for years and years have disappeared. I haven’t blocked this person. They’ve checked their iPhone, and all our years of texts are still showing on their phone.

I have an iPad which I usually sync with my iPhone. Before synching it, I checked for my missing texts and they are all still there on the iPad. I don’t want to sync the two devices yet because I think the iPhone will update the iPad and erase them all to match the iPhone status and relating to the texts to that person.

Firstly, I’d like to understand why the messages disappeared on the iPhone.

Secondly, I’d like to know if I can get the messages back on the iPhone, which are currently still intact on the iPad?

I’m not tech savvy, so I’m wondering if there is an answer that I can manage to work through or if I need to take my phone into a specialist.

Thanks, Dianne

[Re-Titled by Moderator]

Original Title: Text messages disappeared.