I've observed it once. Restart LR seems to make the problem go away at least for a while, and doing Preferences > Performance > Camera Raw Cache Settings > Purge Cache may make the problem go away for even longer.
Please add your details of what you've observed to the bug report, and be sure to click Like and Follow at the bottom of the first post. That will make it a little more likely that Adobe will prioritize a fix, and you'll be notified when the bug's status changes. Without more reports from users, Adobe will ignore this issue.
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