Unable to pin a specific message thread after iOS 18.3.1 update

I have an iPhone 15 Plus and I upgraded to iOS 18.3.1 about 2 days ago. I noticed after the update one specific text thread will not remain pinned. If I pin it, it will stay as long as I’m still in the messages app. If I close the app it goes back down to the bottom with all the other unpinned text threads. I’ve tried to reboot my phone but that doesn’t help. Is the only solution to reset my phone and use a previous backup from before the update? This isn’t a major issue but it is annoying.