There are a number of gotchas with LR capture time -- some are user mistakes and most are LR bugs. If Califdan's suggestions don't help, then very possibly we can identify the issue and likely workarounds:
1. In Library, do the menu command View > View Options and set Compact Cell Extras to:
View attachment 20184
2. Ensure the menu items View > Sort > Capture Time and > Ascending are checked.
3. Scroll until you identify two thumbnails that are not correctly sorted.
4. Post a full-resolution screenshot
of the entire LR window.
5. For each of the two thumbnails, select the thumbnail and post a screenshot of the top part of the Metadata > EXIF panel, including the Date Time fields, e.g.
View attachment 20185