Attention fellow iPhone users, if you have any precious photos nestled inside text messaging threads, be careful not to delete those threads, even if you have saved those photos to your camera roll. Otherwise, you risk losing those pictures forever. The culprit is a weird bug in iOS 15 and/or iCloud, and as of the latest incremental beta update,

Source: Hot Hardware – This Widespread iOS 15 Messages Bug Permanently Deletes Your Saved iPhone Photos