Unable to read text messages on iPhone

For a few primary contacts, I am having trouble reading / receiving text messages.

I will receive a notification of a new message on my Lock Screen or while in another app, but as soon as I tap through to review it in Messages, all I see is a blank screen with a loading icon. Screenshot attached.

Interestingly, I have access to the entire conversation on my laptop Messages app. Which is great, but obviously still poses a problem when I'm out and away from my computer.

Also of note: I transferred to this phone from an android (Pixel 2), and was told that this it just may take a matter of time for old texts to appear or populate. I had a support chat, and I was told it could take upwards of a week for everything to show up. But now it has been well over that time — months — and while some conversations did indeed populate, a few key ones are still not displaying.

I've seen similar questions being raised, and I've taken advice give on them: My phone is not on Low Power Mode, It was enough storage capacity, and it has been recently restarted. Happy to try anything else.